ICS (Infinite City Sprawl) will work on any level. It's most powerful on huge pangea maps with minimum civs where you have time and space to set up your settler flood. It's definitely overkill on Chieftain. It works on Deity if you have practice with it, because you have limited time before the AI makes it to rifleman. The idea is to kill the AI early in the game and/or to create a settler flood (100's of settlers)and get domination mostly without warfare. You can have 100's of settlers on their way to build cities, or (on a smaller map) stop producing all those settlers earlier and mass produce horseman. For the settler flood, if there is a hill in the middle of grassland, you want to build ON the hill (more food in the city radius). You want the cities a little more than 2 tiles (1 tile in between city centers) away from each other in every direction. Mine ALL grassland, as irrigation wont be needed. Don't build improvements (except maybe barracks). Try to buy as many workers as you can, so you aren't wasting population building workers instead of settlers. Have workers mining and building roads. By having roads in place your settler can build a city in the same turn it was created (or very next turn) instead of wasting 4+ turns moving on unroaded tiles.
With every city building settlers and those settlers building another city ASAP, you will easily surpass the AI in # of cities quickly. If you have 4 times as many cities you will only need 1/4 of your cities building a temple to match the culture of the AI that builds a temple in ALL of his cities.
You want to build chariots (hopefully), or horseman in between settler production. Get the Great Library (yes it is possible, you just have to micromanage, so you have a city productive enough to do it - HINT: Join settlers from nearby cities to get that city up in population fast), set science to 0% and when the AI gets you Chivalry use all that money you saved up for a massive upgrade to Knights (only need 1 barracks for the upgrading). No AI will last against 100+ knights just a few turns after they get knights themselves. And with all those victorious knights you will get alot of leaders to rush any wonders you want.
Or, depending on difficulty level you can strike before knights with a ton of horseman (preferably Veteran). Or instead of waiting for the AI to get chivalry, research it yourself.
Most, if not all of the AI should be dead by the time anyone gets to rifleman. If anyone does survive, just disband some of those cities to allow the others to get bigger to produce the bigger items (like tanks).