Why were the mandalorians afraid of the empire?

The mandalorians are the one group of people that you would think wouldn't put up with imperial oppression but instead they cowered at the very mention of the empire. Why were the mandalorians so afraid of the empire. During the mandalorian wars they conquered most of the outer rim and nearly brought the republic to it's knees. And yet they're afraid of the empire. That doesn't make much sense. True the mandelorian wars was almost four thousand years before the films. But they don't seem to have changed that much since then. Of course eventually they tell the empire where they can stick it but only after the empire has been around for almost two decades. Anyway I was just surprised to see mandalorians afraid of anything. via /r/StarWars https://ift.tt/2WDtCFb