How could great empires like America fall flat on their face if there was no God? We know there's a God who keeps order.

The roman empire had to fight through multiple epochs of kings, and tyrants. Multiple bloody civil wars and coups before they were ever an international player, And dozens more before they were considered an empire.
The "1000 years" was in name only there was barely more than one or 2 centuries where it even resembled the previous iterations.