Silla(Korea) and Tang(China) joined forces to defeat Goguryeo. You see, Tang China by itself could not beat Goguryeo. It needed to form an alliance with Silla which was just as militarily powerful as Goguryeo. Chinas goal was to weaken Silla and Goguryeo and then to absorb both countries once the war was over. Silla defeated Goguryeo and Tang tried to swallow Silla.
It culminated in the Silla-Tang war in which Goguryeo and Baekje(another Korean Kingdom) joined forces and wiped out the invading Chinese army.
Silla
Long story short: China get its butt kicked yet again. How embarassing.