Western Roman Empire

The Western Roman Empire was a historical nation-state on Earth, established by order of Emperor in 285 CE, and falling to a succession of invasions in the late 5th century, ending by historical convention with the overthrow of Emperor  by King  in 476.

In the alternate timeline from which the mirror universe split off from, the ahistorical overthrow of Emperor Valentinian III by General Flavius Aetius after the Battle of the Catalaunian Plains led to the empire surviving somewhat longer than in the prime universe.