Total War: THREE KINGDOMS

For this achievement, you have to make 6 unique alliances. It does NOT count if you accept an invitation to an already existing alliance, nor does it count if you accept more members to the same alliance. You can break off an alliance immediately after forming it without incurring any penalties other than the standard negative opinion modifier for breaking a treaty from the former ally. So sign as many treaties with as many people as you can and get your opinion up with all of them. Then just check back every turn and see if anybody's willing to accept a coalition agreement. The AI is generally more willing to go for coalitions then military alliances, but check those too just in case. You should not have to use the grant-administrator-independence/liberate-vassal trick, but you can use it to supplement your process if you need to (you can do it one at a time too, since you don't need to get them all in at once).