civilization-5
In Civilization 5, the game states that the AI gets significant bonuses to their play at the higher difficulty levels. I have been unable to find what exactly those bonuses are. I have heard rumors that on Deity, for example, the AI starts with 3 settlers, 6 warriors, and doesn't have a happiness cap at all.
Can anyone clarify with details?
Military will periodically gift you units. Cultural give you a boost to your per turn culture accumulation. Maritime gives you extra food at your capital, and small bonuses elsewhere.
Which military units you get depends on the age you're in, as does the amount of the bonuses for the other two, so there is a benefit to getting a tech from a new age to increase the bonuses. Being Allied instead of just friendly will also increase the size of the bonus or the frequency with which you are given units.
Its also worth mentioning that regardless of the type of city-state, if you are allied with them, they will give you any luxury or strategic resources that are within their borders. This can be useful to trigger "We love the king" days in your cities to increase the growth rate. When cities demand a resource you don't have, you can use the Diplomacy summary screen to see which city-states have that resource and then consider boosting your rep with them.
Apparently there is a flawless strategy in civ5 and if you apply it correctly, winning on deity is rather easy. And you don't even have to make some special settings for the game. Just I have to warn that its much more fun if you discover it yourself rather than get it from internet, as in that way it kind of ruins your game experience as it did to me to some level.
The easiest way (as Irony Man correctly pointed out) is setting the map type to archipelago, as AI is totally hopeless on water. Just expand all the time, build some naval units to fend off any aggressive AIs, grab those resources, trade and develop. You should be able to get any kind of victory quite easily.
You can also use continents or Pangaea maps. You need to apply a flawless strategy to get a win on those. A strategy might be slightly different depending on which faction you are playing, but there are some basic rules which work for all of them. The specific faction strategy is to get the most of the special ability. That means if you are playing for English - build naval units, if you are playing for French - build a lot of small cities, if you are playing for Romans - build all that is needed in Rome, etc.
The most important bit is a good start. I would divide it into three phases:
Now if you still haven't lost your army at this point you should be doing rather well and can continue playing the way you like. Or if you want to be really effective and crush them all you can apply an ICS (infinite city sprawl) strategy. This strategy is genuine and it works perfectly, but honestly I don't like it myself at all, as it takes all the fun off the game. So if you enjoy Civ5 so far and want it to continue better close this post now, but if you want to further ruin your game experience read on..
The basics of ICS are explained elsewhere much better than I would be able to, so I'll just quote. Here's the theory behind Infinite City Sprawl, as written by alpaca in his Infinite Rome thread on Civfanatics:
The idea of an ICS strategy is to settle cities as close as possible to leverage the additional growth, production and commerce that small cities have over large ones. In Civ5, there are a number of game mechanics that lend themselves well to this kind of strategy. To wit:
1) Maritime city states. The bonus granted from maritime city states is per city. Each adds +2 food to the city tile at the start, increasing to +4 over the course of the game. Since every city benefits from this free food, a single maritime CS ally will allow you to set up two additional specialists in every in the later stages of the game. Obviously, the more cities the better, because each gets the bonus.
2) Happiness buildings. In Civ5, happiness is global... or is it? In fact, only the consumption of happiness is really global. The production is local. Each city can build happiness buildings, and the low-tier buildings are more efficient and more effective than the higher ones. If you have lots of small cities, each can have a Colosseum and a Circus where available, and some theatres. This actually rules out happiness as a long-term limiting factor and turns it into a growth-limiting factor because you need to set up these buildings in each new city.
3) Purchasing things with gold. Provided you have enough gold, you can buy buildings where and when you need them. Spamming trade posts is a typical strategy, and it's possibly even better in ICS. Just spam trade posts, make money, and buy the buildings you need. This is especially good for the more expensive buildings which have a better gold/hammer ratio.
4) Certain policies, like Communism and much of the Liberty tree, scale with the number of cities. So do some civilization abilities or buildings, like the one of Harun al-Rashid or the Chinese Paper Maker. For them, you also want as many cities as possible.
5) Research favors large empires because a tech will cost the same, no matter how many cities you have. Since having more cities usually means having more science, you will tech faster.
6) Trade route maintenance makes you want to put your cities as close together as possible. City tiles are free roads, after all.
There is a significant drawback to ICS which I won't hide from you: The speed of unlocking social policies. This is the only thing that is really better for small empires because, roughly, your average culture per city is what determines policy speed. Since there are sources of culture that don't scale with the number of cities, like wonders and cultural CS, you will be slower at unlocking these SPs, so make sure you only pick those which are most useful to you.
You can find some great comprehensive examples of how it is applied here: http://www.garath.net/Sullla/Civ5/liberteordre.html or here: http://forums.civfanatics.com/showthread.php?t=390302 and this one is very short and straight to the point: http://forums.civfanatics.com/showthread.php?t=388793
Best Answer
There are too many things to list out here, but you can find the answers in the CIV5HandicapInfos.xml file in your \Steam\steamapps\common\sid meier's civilization v\Assets\Gameplay\XML\GameInfo folder. For example, Deity lists that the AI starts with two defensive units (warriors), two workers, and one scout. Another part of that file lists the free techs for you or the AI. On Deity, the AI starts with The Wheel, Mining, Animal Husbandry, and Pottery.