It has been the fate of every great empire of the past to be subjugated and destroyed by powers which were once its vassals or colonies.
The Persian Empire was captured by its former vassals, the Macedonians (led by Alexander the Great). The Roman Empire was captured by its former vassals, a coalition of Central Asian and European barbarian tribes led by the Visigoths. The last traces of the Byzantine Empire were captured by the Ottomans, who were once the vassals of the Byzantine Emperors. The Arab movements, which ruled Southwestern Europe (the Iberian Peninsula—Spain and Portugal) for almost six hundred years (711 to 1492), were initially being supported by the Byzantine Emperors and the political establishment in Italy. The Zengid Empire was replaced by Saladin’s Ayyubid dynasty (the Zengid ruler Nur ad-Din was responsible for the rise of Saladin). Ayyubid dynasty was replaced by the forces led by their former slaves, the Mamluks, who established the powerful Mamluk dynasty. The Mongol Empire was captured by the powers that arose in their former colonies of Russia and China. The Ottoman Empire was dismembered, between the eighteenth and twentieth centuries, by a series of coalitions in which its former vassals and colonies played an outsized role.
In the next 50 years, the colonial powers could get colonized by the people from their former colonies. Spain, Britain, France, Germany, and Italy could be captured by the forces from North and South Africa, the Middle East, China, Russia, and even South Asia. The American Empire, which has been dominating the world since 1945, could be captured by the forces belonging to South America, Africa, and the Middle East.