Total War: Warhammer III

This is best done with Xiao Ming's faction, as she starts closer to Wei-Jin. Wei-Jin is the capital of Cathay, the floating fortress at the northern end of the Great Bastion. It is held by a faction that is in good standing with you, so instead of conquering it (which is the quickest way if you are just after the achievement), you should concentrate on being friends with them and then confederating them.
For that fight their enemies, i.e. Chaos, make them gifts, ally with them and if you don't have a military access agreement, do not step into their territory. I got them after my first soul without trying too hard for it.

Edit: This was written pre-Immortal Empires. Based on MaouZombies experience, it does not seem to unlock in the Immortal Empires campaign. You will have to do it in the Realms of the Chaos Gods campaign.