The Western Jin (266–316) was established as a successor state to Cao Wei after Sima Yan usurped the throne, and had its capital at Luoyang or Chang'an (modern Xi'an); Western Jin reunited China in 280, but fairly shortly thereafter fell into a succession crisis, civil war, and invasion by the "Five Barbarians (Wu Hu)." The rebels and invaders began to establish new self-proclaimed states in the Yellow River valley in 304, inaugurating the "Sixteen Kingdoms" era.——Wikipedia  @en