I was defending my recently taken capitol city of Jalmarys, after recently losing my army in combat. The city has 80 defenders and a Western Empire grand army of 300 men came to siege it. I spoke to the leader of the enemy army as he lay siege and convinced him to join the Southern Empire, I was able to get to the offer stage and right as I accept the offer the game crashes. This has happened both times I've restarted and loaded the game, I don't think I am able to make him switch sides without the game crashing.