Games like Galactic Civilizations IV

If you finished Galactic Civilizations IV, the closest matches are Sid Meier's Civilization II, Age of Wonders: Planetfall, Terraformers, Warhammer 40,000: Gladius - Relics of War and Master of Orion II: Battle at Antares. All 8 share its strategy genre and are ranked by how closely their themes and modes overlap.