[shaboinkin]

Unchecked aggression tends to lead to more aggression if you just glance at history. Nazi Germany, Imperial Japan, Spanish invading the Americas, US pushing out the Natives, Roman Empire into Europe, Genghis Khan. It stands to reason that if there was an equal or greater opposing force for the acts of aggression and expansion all throughout history, the rate of expansion would be severely limited. I don’t know much about the Crusades but that seems like a candidate for a stronger force stopping a weaker force from invading parts of the Middle East.