Cao Cao
In 211, Cao Cao engaged a coalition of northwestern warlords led by Han Sui and Ma Chao at the Battle of Tong Pass. Ma Chao and others agreed to make peace with Cao Cao on two conditions. Firstly, Cao Cao had to give up the northwestern territories to them. Secondly, Cao Cao had to grant them official titles. Jia Xu suggested that Cao Cao pretend to agree to their terms, and then try to sow discord among them. Cao Cao heeded Jia Xu's advice. When internal conflict broke out between Han Sui and Ma Chao, Cao Cao took advantage of the situation to attack them and achieved victory.