There were many factors that contributed to the decline of the Western Roman Empire, including political instability, economic problems, military weakness, and barbarian invasions. One of the most significant factors was the rise of rival claimants to the imperial throne. After the death of Theodosius I, there was a power struggle between his two sons, Arcadius and Honorius, who became the emperors of the Eastern and Western Roman Empires, respectively. However, there were also other claimants to the throne, such as the general Stilicho and the usurper Constantine III. These rivals often fought each other for control of the empire, which weakened the central government and made it difficult to defend against barbarian attacks.
In 476, the Western Roman Empire finally collapsed when the barbarian leader Odoacer deposed the last Roman emperor, Romulus Augustulus. However, even after the fall of the Western Roman Empire, there were still rival claimants to the imperial throne. The Eastern Roman emperor Zeno claimed to be the rightful ruler of the entire Roman Empire, but he was challenged by other claimants, such as the Ostrogothic king Theodoric the Great. These rival claimants continued to fight each other for control of the empire until the 6th century, when Justinian I reunited the Roman Empire under his rule.