Then another powerful Chinese dynasty, the T‘ang, came into being, which attacked and crushed Corea, and in the seventh century Liao-tung was again annexed to China.  Meanwhile the tribes in the north, the progenitors of the Manchus (originally spoken of as Sishun and Suchen), were becoming sufficiently civilised to form themselves into one or more organised states, known successively as Fuyu and Yilow, then Wuchi, and finally Mogo, which split up into two, Heishui, or Black Water, in the north, and Sumo in the south.  The last-named developed into a powerful state called Bohai, which was recognised by the Chinese Emperor early in the eighth century... In the tenth century a powerful tribe called Ketans dispossessed the Bohai. (James)