Bearing the previous text in mind, which part of the Roman Empire survived until the fifteenth century? The causes for the collapse of the Roman E...

Bearing the previous text in mind, which part of the Roman Empire survived until the fifteenth century?

The causes for the collapse of the Roman Empire are several, being the invasion of Barbarian tribes the most straightforward theory. Although Rome had fought against Barbarian tribes for several centuries, it was a sequence of raids against it which led the Empire to fall apart.
The West Roman Empire
The North Roman Empire
The South Roman Empire
The East Roman Empire
The British Roman Empire