Call of Duty: World at War, the latest first person shooter sequel developed by Treyarch Invention, has been released via Steam, Valve announced. Call of Duty: World at War takes place in the Pacific theatre (and partially in Russia's advance into Berlin). In addition to introducing franchise-first four-person cooperative gameplay, Call of Duty: World at War serves up a host of new enemies/tactics and a cache of weapons, like the flamethrower.