Roman emperor
The Western Roman Empire collapsed in the late 5th century. Romulus Augustulus is often considered to be the last emperor of the West after his forced abdication in 476, although Julius Nepos maintained a claim recognized by the Eastern Empire to the title until his death in 480. Following Nepos' death, the Eastern Emperor Zeno abolished the division of the position and proclaimed himself as the sole Emperor of a reunited Roman Empire. The Eastern imperial lineage continued to rule from Constantinople ("New Rome"); they continued to style themselves as Emperor of the Romans (later βασιλεύς Ῥωμαίων in Greek), but are often referred to in modern scholarship as Byzantine emperors. Constantine XI Palaiologos was the last Roman emperor in Constantinople, dying in the Fall of Constantinople to the Ottomans in 1453.
Sack of Rome (410)
The sack was a culmination of many terminal problems facing the Western Roman Empire. Domestic rebellions and usurpations weakened the Empire in the face of external invasions. These factors would permanently harm the stability of the Roman Empire in the west. The Roman army meanwhile became increasingly barbarian and disloyal to the Empire. A more severe sack of Rome by the Vandals followed in 455, and the Western Roman Empire finally collapsed in 476 when the Germanic Odovacer removed the last Western Roman Emperor, Romulus Augustulus, and declared himself King of Italy.