I managed to put the game in an infinite loop with some simple XML changes. In my mod I added +1 from Citizen to both Caste and Public Works. If any player (Human or AI) tried to adopt those 2 civics in the same turn, the game entered into an infinite loop. When I replaced the +1 (and +1 ) from Citizens in Caste to just +1 , the game proceeded flawlessly. I think adopting the 2 civics in different turns did not break the game but didn't test that thoroughly, just what I saw in the log files.