It is easy to win on deity if you start conquering other civilizations. Each civilization has its own advantages and you need to make use of those.
First build 8-10 units and then attack your closest AI civilization. Then the next one and so on.
Do not build districts, just build units and take advantage of it early in the game.
You will get districts when you conquer AI cities.
Also if possible you should get your own religion, but only if you are able to get holly sites with +5 or more faith per turn.
AI is pretty stupid/broken, it does build things, but it never makes any meaningful attacks, except early in the game when it has much bigger army then you and sends them all at you.
Winning by taking over AI cities is indeed generally the easiest way to win on deity, as you both take over developed infrastructure (which the deity AI has huge bonuses towards building in the first place), you get more real estate for further expansion of your own, and you are safer in the long run.
You dont necessarily need to go to war with the AI (early on or ever), but I agree that its the easiest way, and personally I (usually) do a late ancient/early classical era war.
That being said, we should be honest here and not claim that "just build 8-10 units and attack" is enough.
A quick (or rather, over explained) guide to early war against the deity AI, for whoever might be interested:
If you want to attack the deity AI (especially early in the game, with the goal of reaping the benefits and get an early lead), you have to consider a lot of variables beforehand such as:
- When do I attack? (Which era/tech level?)
- Where do I attack? (Is there a tactical advantage to be gained from the terrain that I can use? Can I even hold the first few cities on loyalty?)
- How do I attack? (What sort of units should I bring? Are they likely to be obsolete soon? Can I still use those obsolete units to keep pressing? Do I need more ranged units to take out defenders, or are the walls going to be my primary issue so that I need battering rams or siege weapons?)
- How much will the attack set me back? (Producing units takes up valuable production that you could have used for expanding or developing lands/infrastructure. If it fails, I am now even further behind on development)
- Is my attack likely going to be a success? (Requires a very tactical eye and strong tactical understanding, including a good understanding of how damage calculations are done by the engine).
A lot of this just comes down to experience, and every little thing here is very valuable if you want to kill off the AI.
Much more so in the early game (ancient/classical era), because at this point you are slightly behind the AI, and about to be even more behind the AI
unless your attack is a success.
The crucial part is therefore to ensure that your attack
is a success in the first place.
Some important tells to what I usually look for when deciding
if I even want to go for a standard late ancient/early classical era push:
- How much military score does my target have?
This tells me (roughly) how big his army is. Military score is calculated by the cumulative addition of unit combat strength. Meaning that in the ancient era, an AI having 200 military score means that his total army is the sum of units who total 200 combat strength. This equals about 10 warriors (20 CS x 10 = 200), but it might include archers and spearmen too (even scouts and slingers)
- How strong is the combat city strength of his ungarrisoned cities?
This is actually a huge tell on what military tech and the quality of your target's army is. City combat strength scales from the highest base combat strength of the owner's units (with even more if the city is garrisoned and is a capital, which is why you want to look at a base non-capital, non-garrisoned city). Your target's cities will be around 13 combat strength if he has only built warriors, but will go over 20 the second he gets his first spearman out, and even more on the first heavy chariot. If you see a city that has over 30 combat strength, you know that he has built his first swordsman/horseman, without even needing to spot that unit.
If you both see an un-garrisoned city with 30+ combat strength and a high military score (300 for instance), you should just call off the attack right away if you're still on warrior tech and nowhere close to better units. You cannot fight against swordsmen/horsemen, and not that many units.
If he however has cities at 13-20, you can easily stomp both the units you face (warriors, slingers, spearmen), while only having to make sure that you bring enough units to actually take the city before you run out of health to keep the siege up.
- How much science is my target generating per turn? (Even if he has low military score and low city combat strength, if he has 40 science per turn, you can expect to meet swordsmen real soon, which is another thing you have to factor in. While if he has "only" 20 science per turn, you generally have more time to attack)
Once I have evaluated the factors above (which decide whether or not I think a war is a viable path in the first place), I now need to evaluate
how I should attack.
There are a myriad factors at play here, but one of the most important ones it to understand which combat strength modifiers I have available myself, vs what the AI has. Some examples:
Your bog standard 20 CS warrior is going to be heavily outclassed by the AIs initial +4 CS (=24 CS) warriors in a plain 1v1.
But there are other ways to increase that combat strength, and that is by either by having a leader ability/unit that gives you an edge (Aztec eagle warriors for instance are 28 base, stronger than deity AI warriors, or +3 from playing as black queen Medici, giving you 23 CS warriors),
or abusing terrain/fortification to make the AI take bad trades.
Being attack while standing on a hill gives your warrior +3 combat strength, making it almost as strong as the deity AI (23 vs 24), while the same is true for forest/jungle. If you stand on a forested hill however, that gets doubled to +6, which means that the deity AI is now taking the bad trades if he attacks into you (which the AI will usually do, because its dumb).
Now if you
fortify on a position like that as well, you gain
another +3 on top of that! And if you keep fortifying the turns after that, it too gets doubled to +6 CS!
You can use that to your advantage, and thus try to fortify on key positions (hills, forest/jungle, or ideally both), to gain upwards of +12 CS on top of your base 20, which
easily makes you trade super well against the AI (as well as healing you for +10 per turn in neutral territory, or +5 health in AI territory).
Using tactical advantages such as these can easily bleed the AI dry in a pure warrior vs warrior engagement, even if the deity AI has a numerical advantage in both warriors, and base combat strength.
You can even use a personal trick of mine that I like quite well, which is to promote the unit
after choosing to fortify and heal (like you usually would do against the AI).
You do this by fortifying and healing (thus maintaining your bonus CS from fortification), cancelling the unit's orders manually, and only
then choose that unit's promotion.
This maintains the units fortification bonus, heals your unit for +50 health (as well as giving you a promotion bonus), as well as additional fortification healing on top of that.
This also works with pillaging, which is especially useful when pillaging farm for +50 health.
Choose fortify and heal, manually cancel it, and only
then do you choose to pillage that tile.
There is never a reason to not use this trick when pillaging anything with a melee unit , because you're gonna use up your 2 movement points anyway, so you might as well keep your fortification bonus and the extra healing from fortification.
The factors above will help you win on the tactical level, and is often the deciding factor on whether or not an attack will succeed or not.
Note that it's not always a bad thing if there are no forested hills around the target's city - this can often be an advantage too.
While you do take more damage from being attacked, it also means that any archers/siege units behind them can stand safely behind a warrior and shoot at the city/enemy unit, without fear of being attacked directly.
But, just "ramming 8-10 units down their throat" will generally not be enough vs the deity AI, because the AI trades better than you in a 1v1 scenario of equal units, and because they usually have more units than you as well, so anyone seeking to engage in warfare should definitely keep factors such as these in mind.
The last factor is attacking cities as well (once you have generally subdued his army).
Can your warriors expect to take out the city?
Against cities that have +10 or more combat than your attacking melee units, I would say no, don't even bother unless you have archers/siege units to shoot at the city (which will slowly whittle it down).
You have to figure out the sweet spot here yourself, but the more combat strength a city has, the more units you need to bring (especially if you are gonna attack with melee units), because your units will eventually run out of health (to maintain the siege, where the city cant heal back any lost health) if you bring too few of them.
I generally dont attack with less than 6 warriors and (often) 2 archers (and often a battering ram, just in case) when a city is at 20 combat strength baseline, because there is a chance that you run out of warrior health and/or enemy reinforcements force you to disengage from the siege, before that city falls.
Which is catastrophic on deity, because if you cant take the first couple of cities with your initial push, you are even further behind the AI, and its just a matter of time before he gets walls up (if they arent already), he outtechs you and starts fielding even better units than you.
Hope this is somewhat helpful, even though it describes an ancient/classical era push.
Most of what I wrote here should be applicable regardless of era though.
Just try to get a routine down on whether or war is a good choice (checking target's military value and city combat strength), and then how you should be attacking (tactically speaking).
