You’re talking about the “Power of Three” achievement in Throne: Kingdom at War.

You unlock it by attacking three different target types in a short time window:

one resource tile

one Assailant / neutral enemy

one other Lord’s town

Best way is to find all three close together on the map and send small, fast marches (even 1 troop) to each one quickly so all attacks land within a few minutes. Once all three hits register, the achievement should pop.

By the way, when I’m not grinding achievements I’m usually checking menu and price info here:
https://mcd-breakfast-menu.com/ 

You get Power of Three by having three buildings all upgrading at the same time.