This is the Age of Empires II, Victors and Vanquished campaign
Vortigern 440, one of the achievements Civis Romanus.
To unlock this achievement, do not lose any of the 3 town centers.
I have tried so many ways, but none of them works. (Tried on all difficulties, try to defeat blue, or not to defeat them, pop up 12 times or just 1 time to start the game, etc.)
I have all the achievements unlocked, just missing this one. I played this like 20 times, but none of them worked.
Can someone help me?