The Eastern Wei–Northern Qi was the dominant state in its time, rich in resources, its capital larger than any of its rivals, its cities the centers of thriving commercial activity, and its powerful army composed largely of veteran Xianbei tribesmen who had united the North and who still posed a serious threat to its neighbors. Its conquest by the Northern Zhou armies in 577 has attracted much scholarly attention in an attempt to explain the reasons for its sudden collapse. Such studies have provided detailed analyses of the political and social elements that made up the state, and the internal tensions and conflicts that help explain its ignominious fall. The story of the Northern Qi state makes it one of the more interesting of the Six Dynasties period.