I believe one would find that Rome was a republic for their first five centuries.. (about 500 BC to 25BC) .
..And an empire for their last five centuries (about 25BC to 475 AD)
Repulic 509 BC-27BC, Unified empire 27BC-395AD.
In 376, a large migration of Goths and other non-Roman people, fleeing from the Huns, entered the Empire. Roman forces were unable to exterminate, expel or subjugate them (as was their normal practice). In 395, after winning two destructive civil wars, Theodosius I died. He left a collapsing field army, and the Empire divided between the warring ministers of his two incapable sons. Goths and other non-Romans became a force that could challenge either part of the Empire. Further barbarian groups crossed the Rhine and other frontiers. The armed forces of the Western Empire became few and ineffective, and despite brief recoveries under able leaders, central rule was never again effectively consolidated.
Sound familiar?
Sure does, but of course those cagey Romans had already moved the capital of the Roman Empire from the city of Rome, to
Constantinople (333 AD).
....And Old Constantine escaped to the city named for himself and went on to rule for a while.
Today that city is called Istambul, and is part of modern day Turkey.