>>18138892 (OP)
During the Three Kingdoms Period, one of the warring Korean states Silla allied with Tang to destroy it's competitor. Think it was Balhae. Silla was the ultimate beneficiary as it swallowed up all that extra land and Chinese manpower did a lot of the world.
Then when the Tang tried to turn Silla into a proper annexed state Silla fought back and got the better status of independent tributary. It's like shit straight out of a Paradox campaign. Use your allies to win your wars of conquests for you.