Meng Tian
The Xiongnu in the north had been a threat since the Qin dynasty. Qin Shi Huang had sent the general Meng Tian to oversee the defences on the Qin Empire's northern border and the construction of the Great Wall to repel the invaders. Meng Tian achieved success in deterring the Xiongnu from advancing beyond the border. However, after the Qin dynasty collapsed, the Xiongnu seized the opportunity to move south and raid the border again. In 201 BCE, Hán Xin (King of Hán) defected to the Xiongnu leader, Modu. In the following year, Emperor Gaozu led an army to attack the Xiongnu but was besieged and trapped by the enemy at the Battle of Baideng. Acting on Chen Ping's advice, he bribed Modu's wife with gifts and got her to ask her husband to withdraw his forces. Modu did so. After returning to the capital, Emperor Gaozu initiated the policy of "heqin", which involved sending noble ladies to marry the Xiongnu leaders and paying annual tribute to the Xiongnu in exchange for peace between the Han Empire and the Xiongnu.