Early modern period
In the early modern period, the Holy Roman Empire was a union of territories in Central Europe under a Holy Roman Emperor the first of which was Otto I. The last was Francis II, who abdicated and dissolved the Empire in 1806 during the Napoleonic Wars. Despite its name, for much of its history the Empire did not include Rome within its borders.
Christianity in the 4th century
Disunion in the Roman Empire further contributed to disunion in the Church. Emperor Diocletian 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 I, who established Christianity as the official religion of the Roman Empire, died in 395 and was the last emperor to rule over a united Roman Empire; following his death, the division into western and eastern halves, each under its own emperor, became permanent. By the end of the 5th century, the Western Roman Empire had been overrun by the Germanic tribes, while the Eastern Roman Empire (known also as the Byzantine Empire) continued to thrive. Thus, the political unity of the Roman Empire was the first to fall.