As I pointed out, Rap, in the REAL world EVERYONE loses sometimes, and that's what makes the real world so interesting.

Roman commanders sometimes made terrible errors that led to terrible defeats. The destruction of Varus' legions by the Germans was one case of that, and the massacre of Crassus' army by the Parthians was another. The Parthians were indeed a deadly force, specially when you fought them on their own ground and on their own terms. They weren't so good at carrying out siege warfare, but on open ground they were a terrible foe.

What eventually defeated Rome, though, was their own overweaning ambition. They conquered so large an empire that they could no longer afford to administer it, garrison it, and maintain it. The same thing, I think, is happening to the USA at the present time. Like Rome, the USA has overreached itself. It happens to most (if not all) great empires at some point...they reach a bit too far. They make a few too many enemies.