The population of your civilization (only yours) will have a population of 300. Also if you want to do the same cheat for the other civilizations just enter "everybody has 200" (but the thing is that they'll only have 100 population limit.)

Also here's another cheat is "Iron man.", and what that does is an army of 15 U.S M-34 Tanks that shoot rockets and have a big machine gun that fires really fast.