Call of Duty: World at War is a first-person shooter set during World War II, focusing on the Pacific and Eastern Front theaters. The single-player campaign follows two perspectives: U.S. Marine Private C. Miller fighting against the Imperial Japanese Army across islands in the Pacific, and Soviet Red Army Private Dimitri Petrenko advancing from Stalingrad to Berlin. The game features more graphic violence than previous entries in the series, including limb dismemberment and destructible environments. Multiplayer retains the leveling, perk, and killstreak systems from Call of Duty 4: Modern Warfare. The game also introduced the cooperative Nazi Zombies survival mode, in which up to four players fight increasingly difficult waves of undead while purchasing weapons and unlocking new areas.