 In the spring of 211, Cao Cao sent the commander Zhong Yao to the Wei Valley, ostensibly to attack Zhang Lu's theocratic state of Hanzhong.The incursion provoked the northwestern warlords, including Han Sui and Ma Teng's son Ma Chao, into forming a coalition to resist Cao Cao.The coalition opposed Cao's forces in the Battle of Tong Pass, where Cao personally took charge of operations.