靖康之变
Scholars usually make a historiographical distinction for dynasties whose rule were interrupted. For example, the Song dynasty is divided into the Northern Song and the Southern Song, with the Jingkang Incident as the dividing line; the original "Song" founded by the Emperor Taizu of Song was therefore differentiated from the "Song" restored under the Emperor Gaozong of Song. In such cases, the regime had collapsed, only to be re-established; a nomenclatural distinction between the original regime and the new regime is thus necessary for historiographical purpose. Major exceptions to this historiographical practice include the Western Qin and the Tang dynasty, which were interrupted by the Later Qin and the Wu Zhou respectively.