An army, i dont remember if it was from another Civ i was at War with, a bear or from these grey enteties with a Lightning, outnumbered me and Attacked me. I retreated wich forced me in to the farc of war, where i was suddenly forced to attack an Army from the Olmecs. This triggered a crisis and then a war, wich i gladly took because i just finished my last one. But for a more Peaceful Player it would be a Desaster. 

You probably know this by now, but you (and the AI) can only retreat once. So whether or not you wanted to engage in the second battle, you didn't have a choice.