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.
Roman emperor
This line of Emperors lasted until 1806 when Francis II dissolved the Empire during the Napoleonic Wars. Despite the existence of later potentates styling themselves "emperor", such as the Napoleons, the Habsburg Emperors of Austria, and the Hohenzollern heads of the German Reich, this marked the end of the Western Empire. Although there is a living heir, Karl von Habsburg, to the Habsburg dynasty, as well as a Pope and pretenders to the positions of the electors, and although all the medieval coronation regalia are still preserved in Austria, the legal abolition of all aristocratic prerogatives of the former electors and the imposition of republican constitutions in Germany and Austria render quite remote any potential for a revival of the Holy Roman Empire.