War

Day of Defeat: Source
by Valve
Valve's WWII Multiplayer Classic - Now available for Mac.
Genre: Shooter, Strategy, Simulation, Action 
Linux Air Combat
by Robert Bosen
LAC5.67
(20 Feb 2018)
LINUX AIR COMBAT is a free, open-source combat flight simulator developed by AskMisterWizard.
Genre: Flying / Aviation, Simulation 
Bionic Attack
1.0 (19 May 2017)Bionic Attack is a fast paced Real Time Strategy game set in a post apocalyptic world, where two factions are fighting for the planet domination.
Genre: Strategy 
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(1 May 2017)aa
Genre: Arcade, Point & Click, Shooter, Strategy, Adventure, Role-playing, Simulation, Action 
DDay Normandy
Here is an game who work on linux since very very much time, but it was not instructions to compil the game on this os, it was very difficult.
Genre: Shooter, Action 
Star Conflict
(27 Feb 2013)Star Conflict is an action-packed, massively multiplayer space simulation game that puts players in the role of elite pilots engaging...
Genre: Shooter, Adventure, Simulation, Action 
Gear Up
(28 Jan 2015)Feel the adrenaline as you control your unique tank in multiplayer arcade action! Build your ultimate war machine from over a million...
Genre: Shooter, Strategy, Adventure, Simulation, Action 
Sid Meier’s Civilization® VI
by Firaxis and Aspyr (Mac, Linux)
(20 Oct 2016)
Civilization VI offers new ways to interact with your world, expand your empire across the map, advance your culture, and compete against...
Genre: 4X, Turn-based, Strategy, Simulation