Since Wu and Shu should be allies, head straight to Shu's main camp at the beginning of the battle, making sure to avoid fighting with any of their officers. When you get there, Guan Yu and Zhang Fei refuse to talk, so defeat them both to make sure they do talk.
As it turns out, it appears Wei set things up so both Shu and Wu would fight, with them cleaning up the remaining troops. The battlefield has expanded, with Wei's forces to the north. Wang Yi should be approaching your position, so defeat her and then head over to the eastern side of the map, since Xu Huang will be moving toward Wu's main camp.
Defeat Xu Huang and now both Xiahou Dun and Xu Zhu will appear to attack Guan Yu in the central area. Go to help him out by defeating both of them. This should trigger the central bases across the map to open up, with the officers inside advancing. There's likely to be more officers hanging around the map, but your main objective now is to go and defeat Wang Yi to finish the battle.
|You need to make sure that both bases near your main camp don't fall, which will happen in the second part of the battle. At the beginning of the battle, follow the orders given to you and defeat Guan Yu and Zhang Fei. This will open up the second part of the map, with Wang Yi arriving. Defeat her and then Xu Huang will appear. This is where you need to make sure both camps don't fall, although it's fine if one happens to get captured.|