Age of Empires IV: Anniversary Edition

This achievement can be earned in the 6th mission in the Rise of Moscow campaign called The Great Stand on the Ugra River. To earn this achievement your wooden fortresses must accumulate a total of 50 combined kills before the mission ends. To help speed the achievement up have villagers build up a total of 3-5 fortresses on both North and South crossings.

While they are being built start producing regular archers. Each fortress can accommodate up to 3 archers. Make sure each of them has 3 inside. It also helps to upgrade the fortressed with the double arrow upgrade and the slit upgrades. Prevent your foot soldiers from engaging the incoming waves and let the fortresses take out the Mongolian troops. Have villagers repair damaged fortresses for the next waves.

If you want to provoke more enemy units to attack, make sure you don't have any foot soldiers in the giant circles. The game recognizes this as no one defending the crossings and will therefore send units to attack you. The achievement shouldn't take too long to unlock. If you're having trouble with the enemy waves you can also construct a wall in front of the fortresses so the enemy doesn't damage them. Have villagers repair walls/gates after a wave has been decimated.

Hope this helps you guys out.
Cheers!