Huns

Basically conquered the entire Roman Empire. They were very barbaric, and frequently unkind to Christians.

The most famous leader of the Huns was Attila (406-453), the "Scourge of God", who having put the Balkans (to the very walls of Constantinople), France, and northern Italy, to fire and the sword, and then extracted tribute from the Romans to not ravage them any more, expired from a surfeit of alcohol and a nosebleed at his wedding. The incidents surrounding the Huns are an obvious example of the ways God simultaniusly saves and punishes his followers. Attila would have destroyed Christianity but for the grace of God.