Games like Space Empires III
Games like Space Empires III include Stellaris, Sid Meier’s Civilization® VI, Sid Meier's Civilization®: Beyond Earth™, Heroes of Might and Magic: Olden Era, and XCOM: Enemy Unknown. We matched them by the tags players give Space Empires III on Steam (Strategy, Retro, Turn-Based Strategy, Turn-Based Tactics, and 4X): closest matches first, and among equally close ones the better-known games.

Stellaris
Shared: Strategy · 4X · Grand Strategy

Sid Meier’s Civilization® VI
Shared: Strategy · Turn-Based Strategy · 4X

Sid Meier's Civilization®: Beyond Earth™
Shared: Strategy · Turn-Based Strategy · 4X

Heroes of Might and Magic: Olden Era
Shared: Strategy · Turn-Based Strategy · 4X

XCOM: Enemy Unknown
Shared: Strategy · Turn-Based Strategy · Turn-Based Tactics

Battle Brothers
Shared: Strategy · Turn-Based Strategy · Turn-Based Tactics

MENACE
Shared: Strategy · Turn-Based Strategy · Turn-Based Tactics

Xenonauts
Shared: Turn-Based Strategy · Turn-Based Tactics · Strategy

Sid Meier's Civilization® V
Shared: Strategy · Turn-Based Strategy · 4X

XCOM®: Chimera Squad
Shared: Strategy · Turn-Based Strategy · Turn-Based Tactics

ENDLESS Space™ 2
Shared: Strategy · Turn-Based Strategy · 4X

BattleTech
Shared: Strategy · Turn-Based Tactics · Turn-Based Strategy

Age of Wonders: Planetfall
Shared: Strategy · Turn-Based Strategy · 4X

STAR WARS Zero Company™
Shared: Turn-Based Strategy · Turn-Based Tactics · Strategy

ENDLESS Space™ - Definitive Edition
Shared: Strategy · 4X · Turn-Based Strategy

HUMANKIND™
Shared: Strategy · Turn-Based Strategy · 4X

Sid Meier's Civilization VII
Shared: Strategy · 4X · Grand Strategy

Age of Wonders 4
Shared: Strategy · Turn-Based Strategy · 4X

Warhammer 40,000: Gladius - Relics of War
Shared: Strategy · Turn-Based Strategy · 4X

Xenonauts 2
Shared: Strategy · Turn-Based Strategy · Turn-Based Tactics

XCOM 2
Shared: Strategy · Turn-Based Tactics · Sci-fi

Songs of Conquest
Shared: Turn-Based Tactics · Turn-Based Strategy · 4X

Terra Invicta
Shared: Strategy · 4X · Grand Strategy

Galactic Civilizations IV
Shared: Strategy · 4X · Grand Strategy