The kingdom of Qi was the only opponent of Qin after Qin Shi Huang conquered every other state. King Jian and his prime minister Hou Sheng (后勝), a relation of Jian's wife, sent the Qi army to the western border of Qi to protect the country; but Qin general Wang Ben (王賁), son of Wang Jian, attacked Qi from the north instead and conquered it in 221 BC, completing Qin's unification of China.