AI War:Choosing A Difficulty Level
- 1 How Do I Know What Difficulty Level To Play On?
- 1.1 First Game
- 1.2 Always Play At Or Near The Edge Of Your Skills
- 1.3 How Do I Know If The Current Difficulty Is Too Easy For Me?
- 1.4 Again: Be Sure Not To Play Below Your Skill Level!
- 1.5 That Said: If You're Getting Frustrated, Don't Be Embarrassed To Drop It Down A Notch Or Two
- 1.6 Galaxy Map Size Can Also Affect Difficulty And The Level Of Strategy Required
- 1.7 Further Reading From Player Strategy Guides
- 2 Is The Difficulty Really Constant Throughout A Game Of AI War?
- 3 Like Chess, A Game Of AI War Has Three Abstract "Phases"
- 3.1 Opening
- 3.2 Middlegame
- 3.3 Endgame
How Do I Know What Difficulty Level To Play On?
For your first game, choosing a difficulty is mostly based on your experience with other RTS games, since you don't yet have much experience with this game (hopefully you have played through all of the in-game tutorials already at this point, though -- they are invaluable even if you are an RTS expert in general).
- If you have never touched an RTS game before, and you struggled with the tutorials, you should probably start with difficulty 1 or 2, which will be extremely easy and will give you more time to get used to the game.
- If you have never touched an RTS game before, but you were comfortable with this game by the end of the tutorials, you should probably start with difficulty 3.
- If you have played other RTS games, you probaly should be on difficulty 4 or 5 at the minimum.
- If you are very good at other RTS games, you should be difficulty 5 or 6 at the very least, and you might even want to jump to difficulty 7 right from the start from what we've seen with other players.
Always Play At Or Near The Edge Of Your Skills
The game is vastly more interesting when played at the edge of your skill level, because a lot of the interesting decisions from the game come from you having hard choices. If you play below your true skill level, the game will seem a lot less strategic and less interesting. So if you are relatively confident in your skills, try playing at the upper edge of what you think you can do. You might lose more, but you'll have a more fun time of doing it, and you'll learn more as you play, too.
How Do I Know If The Current Difficulty Is Too Easy For Me?
Once you have played at least one game, or are in progress on your first game, you will be able to better judge if the current difficulty level is too easy for you. In general, the difficulty level is fairly constant throughout the play of the game, so if it is too easy after you have played for an hour, it is not likely to get any harder as you go unless you make a lot of mistakes or the AI does something that really catches you off guard. So you might want to consider restarting with a higher difficulty level after that point if playing below your skill level bothers you.
Signs that the current difficulty is probably too low for your skills:
- You routinely have a large (hundreds of thousands) metal/crystal surplus.
- You don't find the Advanced Research Stations particularly attractive as a goal.
- The AI players never manage to destroy any of your planets.
- You don't find yourself ever struggling with resources or ship cap to defend yourself while also making an effective offense.
- Even with a high AI Progress level (above 600 or 700), you don't find the AI very challenging.
Again: Be Sure Not To Play Below Your Skill Level!
If the AI Difficulty level is too low for you, this is something you will want to correct! Only you know what you are capable of, and where "the limit" is for you will be different compared to other players. If you are playing on too easy a difficulty, it can be a lot like playing Chess against an average ten year old (not Josh Waitzkin or something). If the ten year old is your child, then that's interesting, but otherwise not so much. You'd wonder what all the fuss about Chess was -- it's not really a very strategic game, is it? But when you play at or above your difficulty level, it's a whole other experience.
This advice is true for pretty much all RTS games, of course, but I think it holds particularly true for AI War, since a lot of the strategic depth doesn't come out unless you are playing at a level where the AI is giving you at least something of a hard time.
That Said: If You're Getting Frustrated, Don't Be Embarrassed To Drop It Down A Notch Or Two
To use an analogy, when you take up a sport, you don't go straight to playing it at a college varsity level. Most new players to AI War prefer the 5-6 range to start out, even though the AI is not quite as smart there. This is a complex game, and simply having time to get used to all the mechanics, and figure out strategies, can be a real boon. And hey, the AI is still plenty smart at those levels, it's just not as devious as it can be.
In the end, this is not a competition. It's important to play what is fun for you, rather than just jumping straight into the harder difficulties that the longtime players advocate. It makes no sense to try to immediately compete with people who have logged hundreds or thousands of hours, unless that is fun. Depending on what strategy games you have played in the past, your transition to AI War's unique type of strategy might be faster or slower.
No matter what your past experience, as you play the further, you'll get a more intuitive grasp of how to protect yourself, what works and what doesn't, how to do a quick rush for early planets to protect your economy, and then how to shore up those planets without taking much while you protect those borders. You'll also get a sense for what's an acceptable one-time loss that you can easily absorb and rebuild, and what's something that is going to set you back so far that you're on the path to an eventual loss.
In short: there's no hurry! If you've bought the game, it's yours for life. It's a deep game that can last you many years if you want, so you can take it as fast or slow as tickles your fancy.
Galaxy Map Size Can Also Affect Difficulty And The Level Of Strategy Required
For more information on this, please see What Difference Does The Map Size Make?
Further Reading From Player Strategy Guides
Is The Difficulty Really Constant Throughout A Game Of AI War?
Q: In the text above, it says that the game is supposed to be the same difficulty pretty much the whole time, and so if it is too easy after an hour maybe you should restart. Is this really true? It seems like the game is just easy at first and starts getting tougher and tougher once the planets start to fill up, waves get bigger and the AI's tech goes up... CPAs hitting, border aggression kicking in, etc.
A: The text above is right, but it's also misleading to some extent. It really boils down to how you play the game. If the game is vastly too easy at the start, its unlikely to get that much harder. That said, the first hour (or two, depending on how methodical you are) usually boil down to a land grab that is not particularly difficult (in a sense of your being on the edge of death), but which has far-reaching implications for the later game, hence still the need for strategy and intelligence all the way through.
In general, the likelihood of your losing to the AI goes up throughout the entire game, depending -- again -- on how you play. If you manage to turtle yourself and just hide most of your planets behind some bottleneck while you do some spot raiding, then that might not hold quite as true. Or if you throw caution to the wind and just try to capture stuff constantly while not paying enough attention to protecting your flanks, there will come a tipping point past which the AI brutally murders you.
In many respects, the AI Progress is pretty much a self-balancing thing, so that the difficulty adapts to how you play as you go. That said, it's not going to compensate for something that is orders of magnitude too easy or hard. If you play on difficulty 4 and you should be playing on difficulty 7 based on your true skill level, you'd have to be lobbing nukes around and generally running around making colossal mistakes to lose. On difficulty 1, you might not lose even then.
That said, the difference between 7 and 8, or even 6 and 7, is not so great that you'll have a completely lame time if you're playing below your skill level. The game will be more of a breeze, but the AI will still put up a fight. On the flip side, if you go to 7 when you should be on 6, or 8 when you should be on 7, things will seem to go sort of okay for a few hours, and then you'll just always lose sometime during the middlegame, and rarely see the end game.
Not being immediately threatened in the early game is very different from there being no challenge, by the way. You're setting up very long term positioning and strategies, and so is the AI. You have to keep an eye on what you're doing and what they are, or else you'll put yourself in a bad position down the line.
So how can you really tell if things are going too easily in the early game? See the section below, which describes how the typical early, mid, and late games go, broadly speaking.
Like Chess, A Game Of AI War Has Three Abstract "Phases"
Q: The game doesn't seem to have any literal "ages" or anything like some other strategy games do, but players talk a lot about the mid game and the late game and so on. What are those like?
A: AI War, like Chess, is perhaps best thought of in three distinct phases -- despite the fact that neither of these games has any literal delineations (no "okay, the switch has tripped, so it's the endgame now!"), there are vastly different activities being undertaken in each of the three phases of both games (for Chess: opening, middlegame, endgame). We'll divide our discussion of AI War up in the same fashion
At the start of the game, things are comparably easy -- but don't mistake easy for unimportant. Your first half dozen moves in Chess are usually pretty easy, too -- to the point of being memorized/scripted in many cases, which is not true in any fashion for AI War -- but in both games those early moves can set you up well or poorly in terms of position, tempo, material, and so forth. Treating the early game too cavalierly is a leading cause of death later in games.
- Early Land Grab
- Early Scouting
- Early Defenses
- Early Economic Setup
- Trying To Determine The Type Of AI Opponent If Playing Against Random
- In Multiplayer, You Might Start The Earliest Parts Of Specialization Of Players
No matter what your ultimate strategy is going to be during a given AI War campaign, most likely the opening phase of the game is going to be centered around a land grab where you try to take territory to improve your economy, while also trying to gate raid, put up defenses, and otherwise protect your home planet.
Advanced players will generally try to strike as hard and as fast at enemy planets as they can, disabling them before they have a chance to reinforce. This has to be counterbalanced against your need to defend yourself, which can be tricky depending on the map and the AI personality. That's part of why scouting is so important: it lets you identify targets of opportunity, as well as planets that will develop into serious threats if left unchecked, as well as learn about the opposing ship mix in general use, as well as attempting to figure out which AI personalities you might be facing off against.
All of those early information-gathering activities are critical to making good long-term decisions and ultimately crafting a victory. Which planets you choose to attack in the early game might not make a whole lot of difference to how hard the average early game will be, but it can be absolutely critical for how hard or easy the middlegame turns out to be.
Often there are high-level enemy planets right near your territory, and the choice at this stage is whether to attack them early (and thus be over-matched while the other nearby planets all get lots of time to reinforce in your absence), or to just go for the really easy captures and thus let the high-level enemy planets get the reinforcements (often which causes them to be a permanent issue for you for the rest of the game).
Counterbalanced against those concerns of the potential offensive threat of the various nearby AI planets, you have the issue of trying to take planets that will best serve your economy. That means taking planets that are rich and resources, sure, but it also means taking planets in a strategic fashion that they create bottlenecks that help protect your resources. If your planets are constantly losing their harvesters due to inbound AI aggression, then the middlegame is going to be much harder.
If you don't scout at this stage, then you're just playing blind, and that's never good. Ideally if you are on an 80 planet map, you'll get visibility into the nearest 10-30 planets, depending on the type of map and how much effort you put into it. There are so many other critical things to do in the early game (land grab and defenses most of all) that you'll often be too busy to pay much attention to scouting beyond the immediate area around your home planet. That's okay, because the main decision points at this stage of the game almost always involve planets that are 1-3 hops away from your home planet at most. First priority is to "secure your hinterland" and set up a platform for your expansion into the larger galaxy, and then you can make decisions about where to go in the larger galaxy later on.
Rate Of Human Expansion
During the first hour of a game, usually most players will be able to take 3-6 AI planets for themselves with some degree of ease. This is faster than at any other point in the game, but might be slowed down significantly if players decide to take on a high-level planet very early in the game. In the second hour, the players might then take another 2-4 planets on average, usually arriving at between 8 and 9 plants total by the time the opening phase of the game is done.
Of course that all varies by play style, and some players will prefer to be much more defensive and thus taking far fewer planets in total. Or players might find a snug little corner of the map that they decide to clear completely out and thus have a single incoming bottleneck to a smaller group of planets. The defensibility of that sort of bottlenecking certainly makes it a worthwhile thing to consider if the opportunity for that presents itself.
As with all the phases of the game, there isn't one right way to play, so expansion rates will vary quite a lot from player to player. The above is perhaps the average for someone who is neither a turtle nor a rusher, and who is playing against a fairly evenly matched AI opponent on a moderately-tough map, though.
In general, by the end of this phase you probably have between 100-300 AI Progress, hopefully on the lower end of that spectrum.
During the opening of the game, the AI has pretty pitiful waves due to extremely low AI Progress. The waves will grow in size as the opening progresses, but overall they are small enough that advanced players can design automated turret defenses (maybe with a few mobile ships aiding on Free Roaming Defender mode) that will hold off most waves without any need to oversee the battles. Generally this would be incoming waves of a couple of hundred mark I ships in single player.
The AI is far from idle, however. Consider these just probing raids -- they are enough to make you have to spend metal and crystal on defenses, and they may cripple your economy a few times if you are not careful, costing you precious time/resources, but usually they aren't enough to really threaten a loss.
On the other end of things, the AI is also at its weakest point defensively, but it is also at its most concentrated. Depending on the type of map, there are likely only a few planets that are "on alert" thanks to being near your planets. The AI doesn't get very large reinforcements or very many reinforcement points at this stage of the game, but what they do get is likely to be pretty concentrated.
One effective strategy to intentionally prolong the opening of the game -- to your advantage -- is to intentionally put more planets on alert. Thus the AI feels like it has even more territory to defend, but it doesn't have the power to really defend it all quite yet. That can really buy you some time, which is helpful.
Time In Phase, What Causes Move To Next Phase
The amount of time spent in the opening phase really depends on the player and their play style. On average, it's usually going to last between one and two hours. But if the AI is of a very high level or a particularly difficult personality, that's going to make the opening phase shorter.
Generally it is to your advantage as a human player for the opening phase to last as long as possible. The opening pretty much ends when you hit an impasse and can no longer make a quick land grab in an effective fashion, and can no longer defend yourself completely on autopilot (unless you're really lucky or entrenched).
Risk Of Losing
This part of the game is when you have the least buffer between the AI and your home planet, but at the same time it's when the AI is the weakest. It's also the time when you have the least resources, but you also have the smallest territory to defend, which means that your resources can generally be spent more effectively. All of these factors usually cancel each other out in such a way that it's pretty hard to lose in the early game unless the AI opponent catches you just wrong, or a map is particularly brutal, or you're playing against an opponent far above your skill level.
Losses at this stage of the game do happen during normal play, don't misunderstand, but usually not unless they happen to have a big wave of bombers/tanks or ships that pass through force fields, and you happen to be really distracted or careless. In Chess, it would be rather like being caught in the Fool's Mate, the Scholar's Mate, or similar. It's actually easier for that sort of thing to happen in AI War than in Chess, as there are far more than just two common ways for that sort of early loss to occur, but the overall likelihood is still comparably low.
The opening of AI War is essentially your preemptive strike, and you have the definite advantage in your local neighborhood during this time -- but it's also easy to squander that opportunity if you don't make good decisions that set you up for later success. Despite having the advantage, there's nothing cavalier about this phase.
Chance Of Winning
At this stage of the game, you have basically no hope of winning. The AI outnumbers you by a vast amount, and if you try to go for an early victory against the AI (assuming you can even find their home planet at this stage in the game), your ships will be so outclassed that you likely won't make it even past their wormhole. Scratch that -- you'd never make it even past the "core" planets guarding their home planet with any force worth having.
If you even try to go for a win at this stage of the game, you're just wasting your time and squandering an opportunity to set yourself up for a more solid middlegame. The best advice here is typically to just not even worry about defeating the AI, and to just worry about setting yourself up for a later victory (along with making sure that you don't lose in the meantime).
Once you hit a wall with your initial rush of expansion, then the real long-term strategy begins. Of course, everything you did up until now is going to be echoing heavily throughout the rest of the middle-game, so your early strategies have hopefully set you up in a superior situation for the middlegame. If not, prepare to spend the next while trying to dig yourself out of the hole you put yourself into.
This is where the meatiest strategy of the game comes in, so it becomes harder to generalize here. Generally speaking, you'll have identified some desirable targets during the opening of the game (of economic, technological, or just general military value), and you'll pursue those targets. You're likely coming into this phase of the game still not knowing where the enemy home planets are, and still being blind to half of the map or more, so scouting will continue to be of importance.
Perhaps the biggest general goals of this phase would be:
- Definitely try to find at least 3-4 of the Advanced Research Stations.
- Definitely do a lot of knowledge gathering, possibly knowledge raiding, in general.
- Maybe take some more planets for resources, or maybe adopt a resource-efficient raiding strategy if that's your thing.
- Definitely try to find at least one Advanced Factory that you can adequately defend.
- Definitely avoid putting the core and home AI Planets on alert if at all possible.
And then there's a whole mess of other possible goals that might be of huge or insignificant importance, depending on your play style and the map and the situation as you evaluate it:
- You might want to locate the AI home planets so that you can start planning a route to them, or you might not care about that yet.
- You might want to capture some large weapons, like stuff from Fabricators, or Golems, or Zenith Reserves, etc -- or at least have them ready to be captured if you later decide you need them. Or you might ignore them completely, opting for lower AI Progress instead of that extra firepower.
- If Astro Trains are on for the AI, you might take a lot of care to re-route them to avoid having them constantly messing with your defenses.
- In multiplayer, you might be really seriously specializing per player at this stage.
- In solo or multiplayer, you're probably leaning more towards fleet ships or starships by now, possibly with some mix of both.
- You might be spreading out the AI Alert in order to keep the AI from bunching against you too much.
- You might go on an AI-Progress-reducing quest against Data Centers, Co-Processors, and the like.
And so on. There are dozens of capturables, especially if you are playing with The Zenith Remnant enabled, so there are literally more good things that might be helpful to you (and more bad things that might hurt you) than you can possibly hope to capture (or destroy) on a given map. That's part of why having a good picture of as much of the map as possible is important, because even if there are awesome (or terrible) things that you want to react to nearby, there might be more awesome (or more terrible) stuff further out. It's hard to make good long-term decisions when you have incomplete data, to say the least.
You'll also be really focused on defending yourself, but this will be covered more under the AI Activities section for the middlegame.
Rate Of Human Expansion
By this point in the game, you'll probably be down to capturing a new AI planet on average every 45 to 90 minutes or so. This also means that the AI Progress will be going up slower, but by this stage the AI is already a lot more powerful, and as you try to further expand your territory, you're spreading yourself increasingly thin.
Some advanced players on very high difficulties will practically stop capturing new planets all together, except to provide supply for transports or a way for them to capture Advanced Research Stations and so on. Those same players tend to abandon those planets they capture after they get the goods, so to speak, and also tend to focus on data centers to keep their AI Progress as insanely low as possible.
On the flip side, some other advanced players go for an incredibly completionist style of play that can make a single campaign last 40-60 hours or even more, 2x-6x as long as most campaigns should really take. These players tend to take all the planets in a carefully orchestrated strategy that sends the AI Progress sky high (and AI reinforcements, too), but which is managed by careful bottlenecking and incredible defenses. These players might capture 100+ planets in all, but that's certainly atypical.
Both of the last two paragraphs actually reflect very atypical advanced strategies, and one that most players would find boring or frustrating. But those two strategies reflect the extreme polar ends of what is possible in AI War, and what a few hardcore players gravitate to for whatever reasons. Most players adopt a strategy more about moderation, and keep a middling AI Progress and capture perhaps 20-30 planets at most by the end of the middlegame.
During this part of the game, the AI really comes into its own and is more of a threat than ever. You'll run into Cross Planet Attacks (CPAs) every few hours, Border Aggression will start becoming a problem to an increasing degree, and even the general waves will become more of a problem.
Most waves will still be dispatched fairly easily and with mostly automated defenses, assuming that you're keeping up with your gate raiding and creating whipping boys wherever possible, but the risk of a wave being slightly more powerful than you expect and thus overrunning your defenders is ever present. It is possible -- and somewhat common -- to lose whole swathes of planets to this effect.
This is where you need some degree of defense in depth, protecting your softer internal planets rather than just creating a harder outer crust. That in itself is a challenge, though, mainly for reasons of ship cap caused by limited knowledge and resources in general. The more you spend on defense-in-depth, the less you have for your frontline defenses and for your main offensive arm, so this is a real challenge. Some players use basic defenses paired with a mobile fleet that acts on offense except when being withdrawn to defend against a major AI incursion, for instance -- thus keeping things flexible and generally offensive-oriented.
Even on engagements with the AI where you win, individual ships can sneak away and then pose quite a threat if they are not noticed. Sometimes they'll retreat out into the galaxy and then return later with friends (or at a different location), and so it's important to keep an eye on your Threat meter in the upper right of the screen for this reason. Other times a small band of AI ships will break through your outer defenses and rush through your inner core of planets wreaking havoc while you're distracted with the main force.
It's important to watch out for that, especially if there is a lowish buffer between your outer shell and your actual home planet. As in Chess, it's easy to accidentally leave your "king" open and get checked or checkmated when you weren't expecting it. So it's definitely good to make sure that your defenses are generally as automated as possible in most parts, so that you can keep an eye on the overall battle and status of the galaxy, manage your offense, and deal with any breakaway AI ships that make it through to attack you.
During this time the AI is also on serious defensive mode. By 5-6 hours into the game, some AI planets will have been on alert for practically the whole game now, and they will have 4000+ ships in many cases by this stage. The ramifications of that are discussed here. Part of your offensive and defensive strategies will involve keeping an eye on what the AI is doing defensively, and adjusting as needed.
Time In Phase, What Causes Move To Next Phase
The amount of time spent in this phase is really hard to quantify, because (again like Chess) it makes up the bulk of the game. The opening for AI War is a pretty predictable 1-2 hours with relatively fewer exceptions. The endgame is also shorter, as it mostly consists of an assault on the two AI home planets. But the middlegame fills all the rest of that space.
Most games of AI War last for around 9-14 hours on an 80 planet map if you're using non-extreme strategies. On a 40 planet map, it's perhaps more like 7-12 hours on average, and it's a bit longer with even larger maps. The smallest maps are, somewhat paradoxically, neither easier nor particularly faster to play than a 40 planet map.
Some players that are very advanced and use game settings to make a more expedient game can get a faster experience, and those that are really completionist can certainly turn a single campaign into a marathon to rival the length of many RPGs.
The trigger for moving to the endgame is pretty clear cut: the human team decides that they are ready to start attacking one or both of the AI homeworlds. Of course, plenty of games never get to this stage at all... because the humans are already dead.
Risk Of Losing
The risk of losing is actually higher during the endgame phase, but the risk is high enough during the middlegame that a huge number of games never make it to the endgame. If you're playing at a difficulty level in keeping with your skill level, this is a pretty hard game. If you play on difficulty 10 or something else equally insane, it's pretty much Dwarf Fortress hard.
The three main causes of loss in this phase of the game are, in from riskiest to least-risky:
- 1. Getting swept out of the galaxy by a massive cross-planet attack.
- 2. Having a small band of AI ships break through your defenses at some point and checkmate you on the sly.
- 3. Having your defenses unexpectedly overrun while your main fleet is elsewhere, possibly because of killing a high-level AI planet's command station early (with the risks that entails), or because of roaming Threat, Special Forces, the presence of some hostile minor faction, special forces ships, or some combination of the above.
To avoid losing, you want to make sure to do some or all of the following, in no particular order:
- Keep the AI Progress as low as you can, via killing data centers or by only taking targets that are really worth it.
- Keep really good defenses in place, and defenses-in-depth, using lots of turrets in particular, but also mines, fortresses, or whatever else you like.
- If a CPA seems far larger than you can possibly defend against, consider nuking them if a few thousand of them are all on one planet at once. Usually it isn't worth it unless you can get about 3,000 or more of their CPA ships in one blast, but it just depends -- if it's the difference between a loss and surviving, go for whatever works.
- Have as good an economy as possible, so that if your main fleet gets wiped out on the front lines, you can crank out replacements by the time the AI reaches your inner planets. If you're always running yourself at ship cap due to being that rich, you can also invest in mercenaries in the meantime, which expands your forces even more.
- Consider all your options when faced with a seemingly impossible incursion -- use lightning warheads to strike the AI when they are planning to come through a wormhole, use multiple EMPs to stun them before you go in for the kill, use the fleet starships to boost your turrets and/or other ships, try to strike the onrushing AI ships in smaller batches where you outnumber them if at all possible, etc.
Chance Of Winning
Given the definition of the endgame, it might seem to be logically impossible to win in the middlegame (the endgame starts when you decide to go for the AI home planets, and you win by going for the AI home planets). However, it is possible -- if rare -- to be able to win during the middlegame.
Generally there's a pretty defined arc to when you hit the endgame: you've really beefed yourself up to the point where you feel like you'll be unstoppable or close, and you're ready to go kick some AI butt. There's always more that you could do to beef up more, but you're confident and ready.
However, the rare exceptions come in when you notice some sort of opportunity early, and decide to take it. Maybe you just got a golem or a giant zenith reserve cracked open, and the AI Progress is low enough that you want to take a whack at those home planets without fully beefing yourself up to where you'd normally need to be. That's harder than it might sound, even with a golem, because the AI has Mass Drivers, warhead interceptors, ion cannons, and core ships galore on those home planets and the "core" planets around them. So generally you'll need to be very clever and lucky with your main fleet and/or transports to make way for the larger hardware (even starships) that you're intending to strike with.
If you go that route, then your strategies would switch over to the endgame ones for a while -- but if you fail, then you can just go right to the middlegame, lick your wounds and continue beefing up your forces, and then go for the endgame a while (sometimes hours) later.
So you've survived to the point where you think you're strong enough to take out the AI home planets. Now it's time to prepare for the final assault, and then see if all your hard work and preparation will pay off.
You're out to kill the AI home planets at this stage. You know where they are, and hopefully you have scouts sitting on them and other key planets providing you a continuous stream of up-to-the-second intel. You can attack either planet first, or you can even try attacking both planets at once.
There's a huge jump in AI Progress (and often Threat) after the first planet, so it's wise to hit both planets at once if you can do so -- but usually it's a stretch just to get one at a time, even in multiplayer. You'll probably set up a forward base with docks and such 2-3 hops away from each home planet, which will put the "core" planets on alert but not the home planets, and then you'll likely use transports or otherwise carve a path to the AI home planets themselves.
There are a variety of strategies for actually taking the home planets out, but they vary so heavily on what ships you have and how you've built yourself up over the course of the rest of the game that it's even harder to generalize here than it was for the middlegame.
Rate Of Human Expansion
Most likely the only reason you'd take a planet at this stage of the game is for military advantage. In other words, for creating those forward bases 2-3 hops away from the AI home planets. Presumably you already have all the technology you need or want, you already have the resource throughput you desire, and everything is set up for you to try checkmating the AI. Granted, things may go wrong (and often do), so you may need to regroup and get more knowledge or resources or whatever than you thought, but as much as possible the goal is just conquest here.
Everything that was said about the AI during the middlegame still holds true, but the AI will also make special efforts to reinforce its home planet when threatened. If you've kept the AI Progress low and kept the AI home planets off alert until the last possible second, you might actually find the destruction of the first AI home planet somewhat anticlimactic, though certainly not a pushover.
However, this can be quite a false sense of security. Upon killing that first AI, you immediately jump around 100 AI Progress, a bunch of core ships likely go free from that planet and may make a beeline for your home planet (which you may not be watching very carefully at this stage), and if you're playing with AI Plots turned on you might get another nasty surprise of some sort (such as the Avenger appearing and wreaking absolute chaos until you either kill it or hurriedly kill the second AI, whichever seems easier).
One way or another, after you kill that first AI home planet, everything gets a fair bit harder all of a sudden. If you just barely scraped by with the first one, the second one might be even more of a nightmare. That extra AI Progress often pushes the tech level of waves and reinforcements up a notch, which makes your defenses suddenly strained even if they had not been before, and if a higher-level CPA is suddenly declared then you're in real trouble. This is why it's a great idea to be ready to do a one-two punch against both AI homeworlds if at all possible -- though often you just have to roll the dice, since each AI home planet might take 20-60 minutes depending on how well you've set things up for yourself versus how well the AIs set things up for themselves.
Time In Phase, What Causes Move To Next Phase
Really, this is pretty hard to quantify as far as time spent. It might be under an hour, or it might be a few hours. It's generally not a grind-fest, but if you alerted the home planet too early or were more ill-prepared than you thought, then it might turn into one. In those situations you can either cut your losses and regroup for a while, or you can just hammer against the AI with wave after wave.
This phase ends when either you kill both AIs, or they finish off your team. Or sometimes you might revert to the middlegame for a while, but that's less common once you've committed to trying to take out one or both of the AI home planets.
Risk Of Losing
Especially when you consider the normal danger from waves, CPAs, border aggression, special forces, and all that good stuff that's always around (and pretty dangerous by this stage), the time right after you kill the first AI is perhaps the most dangerous time in the entire game. You may have a few hundred core ships streaking towards your home planet right when some other calamity strikes, and that's a good example of when multiple events can combine to cause your defenses to get unexpectedly overrun.
And given that most of your fleet is probably either a) dead from the battle, or b) completely on the other side of the map from your home planet, your ability to bring your mobile forces home to aid in your defense is at an all-time low for the game.
Losing right when you're on the cusp of victory... hurts. So make sure not to get so caught up in your "inevitable" victory that you get stabbed in the back when you're not looking.
Chance Of Winning
This is the part of the game in which you'll win, most likely, if you were going to win. It's still quite hard, make no mistake. Some players that come to AI War from other RTS games think that victory is inevitable when really it is far from it. They look at their thousands of high-level ships, they have scout intel showing that the AI planets are undefended for the most part thanks to not being on alert, and they assume that they can't lose.
This is folly. You can lose at any point, even if you have overwhelming odds. Don't be like the Buggers at the finale of Ender's Game. The AI can -- and will -- do that to you if you're not careful. You could outnumber their home planets 10:1 and still lose horribly because your fleet was in the wrong place and your defenses weren't enough.
So proceed with caution, at any rate. Another wrong assumption that many players of other RTS games carry over to AI War is that the game will get easier once the first AI player is dead. Quite the opposite, as noted above -- AI War is a team game, when it comes to both the humans and AI players. No human or AI players are ever "out of the game" early; the game ends for everyone at once. So when you kill the first AI home planet, all you've done is really make them angry and more powerful, and both of them are still right there ready to kill you (same principle holds true when they kill one of the human players in a multiplayer game). Of course, killing one of their two home planets does get you that much closer to actual victory, so it's a needed step, but it is a very dangerous step.
If you do manage to win, it's a pretty impressive achievement, as this is quite a hard game on the standard difficulty levels. Congratulations!