While the central Song court remained politically divided and focused upon its internal affairs, alarming new events to the north in the Liao state finally came to its attention. The Jurchen, a subject tribe of the Liao, rebelled against them and formed their own state, the Jin dynasty (1115–1234). The Song official Tong Guan (1054–1126) advised Emperor Huizong (1100–1125) to form an alliance with the Jurchens, and the joint military campaign under this Alliance Conducted at Sea toppled and completely conquered the Liao dynasty by 1125. During the joint attack, the Song's northern expedition army removed the defensive forest along the Song-Liao border.