Hangu Pass
In February 190, the Guandong Coalition (關東聯軍, literally: Coalition East of the Pass) was formed after several regional officials and warlords gathered east of Hangu Pass with their armies in response to the call for a punitive war against Dong Zhuo. Yuan Shao was elected to be the leader of the coalition. The forces of Sun Jian and Cao Cao also participated in the campaign under the banners of Yuan Shu and Zhang Miao respectively.