Launch the Battle app and log in to your account. Select All Games. Find and select Call of Duty: Modern Warfare II. Select the Install button to download and install the game.

There's Rimworld with the tribal start (although you'll be fighting/dealing with more advanced factions but you yourself will be at the stone age). There are mods to restrict the whole world in the game to be one age and disable other events.

Once Human on Steam. Once Human is a multiplayer open-world survival game set in a strange, post-apocalyptic future. Unite with friends to fight monstrous enemies, uncover secret plots, compete for resources, and build your own territory.