The three armies of the Jin State set off together, advancing eastward. Duke Wen of Jin personally commanded the army, with Xun Linfu as the chariot driver and Wei Chou serving as the chariot warrior on the right. Grand Marshal Zhao Cui was in charge of rewards and punishments for the three armies. The commanders and their deputies led their respective troops; the commanders of the Central Army and Lower Army were both over forty years old. As for the Upper Army, two white-haired elders in their sixties led the troops.
The first target: the State of Cao.
Why attack the State of Cao? There are two reasons.
The publicly stated reason is that when Duke Wen of Jin passed through the State of Cao years ago, he was sexually harassed by Duke Gong of Cao, leading to a serious loss of dignity.
The real reason: Last year, the State of Cao had just allied with the State of Chu. By attacking the State of Cao, the State of Chu would be forced to come to its rescue.