: In the scenario editor, you can bypass hardcoded limits by using triggers to spawn units directly or by setting native unit caps to extremely high values, as these often do not contribute to your standard population cap. How to Install Unlimited Population Mods
: If downloading from a third party like Steam Community, place the extracted mod folder into: C:\Users\[YourName]\Games\Age of Empires 3 DE\[SteamID]\mods\local . For Age of Empires 3 (Legacy/Complete) Population | Age of Empires Series Wiki | Fandom
There are several popular ways to remove or significantly increase the population limit depending on your version of the game.

