History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously divided the administration of the eastern and western portions of the Empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
Pavia
It was at Pavia in 476 AD that the reign of Romulus Augustulus (r. 475-476), the last emperor of the Western Roman Empire ended and Roman rule ceased in Italy. Romulus Augustulus, while considered the last emperor of the Western Roman Empire, was actually a usurper of the imperial throne; his father Flavius Orestes having dethroned the previous emperor, Julius Nepos, and raised the young Romulus Augustulus to the imperial throne at Ravenna in 475. Though being the emperor, Romulus Augustulus was simply the mouthpiece for his father Orestes, who was the person who actually exercised power and governed Italy during Romulus Augustulus's short reign. Ten months after Romulus Augustulus's reign began, Orestes's soldiers under the command of one of his officers named Odoacer, rebelled and killed Orestes in the city of Pavia in 476. The rioting that took place as part of Odoacer's uprising against Orestes sparked fires that burnt much of Pavia to the point that Odoacer, as the new king of Italy, had to suspend the taxes for the city for five years so that it could finance its recovery. Without his father, Romulus Augustulus was powerless. Instead of killing Romulus Augustulus, Odoacer pensioned him off at 6,000 solidi a year before declaring the end of the Western Roman Empire and himself king of the new Kingdom of Italy.