They had a superior military that was all about discipline but also about merit. Good soldiers were rewarded and bad ones were punished. They were ruthless and would wipe out entire cities full of civilians. The idea was for opponents to surrender. If they surrendered they would be treated well, if they wouldn't then they would be wiped out of existence. This would serve as a message to others who would then surrender or suffer the same fate. They also used winter to fight because the harsh winters were uncommon battlegrounds for other armies.
