Right-click the .exe , go to Properties > Compatibility , and select Windows XP (Service Pack 3) .

Focuses on the "Emperor" faction with 25 new missions.

💡 Focus on expanding your Energy network first; without energy, your shield and terraforming abilities will fail.

Currently, the most reliable way to get the game is through digital storefronts that ensure compatibility with modern Windows systems: Search for "Perimeter: Emperor's Testament."