 Complete the following phrase:  A Tungusic people, the Jurchens, ancestors of the Manchus, formed an alliance with the Song dynasty and reduced the Liao dynasty to vassal status in a seven-year war 11151122. The Jurchen leader Wanyan Aguda proclaimed himself the founder of a new empire, the Jin dynasty. Scarcely pausing in their conquests, the Jurchens subdued neighboring Goryeo in 1226 and invaded the territory of their former allies, the Song dynasty, to precipitate 