The Hate is strong in this one.
I dont know if you got your info from MiniTru, but thats not what happened. The Romans defeated some tribes, but got some major defeats dealt and decided that the wilderness was not worth investing even more man & coins, so they fell back a bit to more defensible positions, build the Limes, and called it a day.
Later (as in ~300 years) they hired more and more germanic tribesmen as soldiers of fortune and took them into the Army, till the Roman Army of the Western Empire was largely run by germans with some roman training. But depending on hired Mercenarys (Foederati) with not exactly shining Loyalty to The Empire was not healthy, and in 476 the remains of the Western Empire were dismanteled by ... tada... a german King, Odoacer.
In the End Roma looked like this:
Thats when The Dark Ages started, which were not a "funtime" for western civilization.