Exactly, my game went to unplayable 1-2fps after trading the world map on a huge world map.Snarfy said:2. "Trading world maps" with other countries.
#2 is quite serious on huge world sizes, and i've got a lot of memory. On my machine, doing one of these near the end of a game when a lot has been constructed results in a crash the next turn. Doing two of these always results in a crash.