Age of Empires IV: Anniversary Edition

This achievement can be done on Mission 7 called The Siege of Wallingford. I suggest doing this on the story difficulty. It's easier and goes by quicker. I suggest building up more villagers and harvesting more resources. Use these resources to upgrade your archers/crossbowmen and build more of them to repel waves of enemies attempting to break down your walls. While being attacked have 2-4 villagers repair the walls that are being attacked so they don't get destroyed.

Hold out enough until the relief army shows up. Mop up the outposts and their defenders at a decent pace. Be careful with enemy towers as they can get onto your walls and attack your archers. I kept my starting infantry by the walls whenever they showed up to defeat melee troops.

After the outposts are destroyed you will be tasked with defeating one more wave of enemies. This shouldn't be too hard as long as it's on the story difficulty. After beating the mission you will get this achievement on the victory screen as long as no walls were destroyed.