While extremely difficult to pull off, nothing is quite as satisfying as dominating nuclear-powered America, Germany and England with nothing but a multitude of cossacks.

Unfortunately the modding scene is rather lackluster (there are many mods, but most are far from finished and those that aren't are buggy and prone to crashing), possibly as a result of the poorly documented expressions (it's executable pseudo-code but seldom behaves the way one would expect - and given some of the bugs in the vanilla game, it seems even the Unciv devs struggle with this).