Call of Duty: World at War is a 2008 first-person shooter game developed by Treyarch and published by Activision. It is the fifth main installment of the Call of Duty series and is the fourth entry in the series to be set during World War II. The game was announced by Activision in June 2008 and was released in November 2008, for PlayStation 3, Windows, Xbox 360, and Wii. Other games under the World at War title were published for the Nintendo DS and PlayStation 2, featuring different storylines and missions. World at War's campaign focuses on the Pacific and Eastern Front theaters of World War II; its story is told primarily from the perspectives of US Marine Raider Private C. Miller and Soviet Red Army Private Dimitri Petrenko. The game's multiplayer component retains several features from Call of Duty 4: Modern Warfare (2007), such as the leveling, perk, and "killstreak" systems. Additionally, World at War marked the debut of the cooperative Zombies mode, which would go on to become a mainstay in Treyarch's subsequent Call of Duty games. Development for World at War took two years and began after the release of Treyarch's previous entry in the series, Call of Duty 3, which was also set during World War II. The game is based on an enhanced version of Infinity Ward's IW engine, with increased development on audio and visual effects. Treyarch utilized the engine to make more parts of certain environments destructible and introduce limb dismemberment and realistic burns to character models. Upon release, World at War received positive reviews from critics, with praise directed at its intensity and violent nature, though it received criticism for its lack of innovation. It became one of the best-selling titles of 2008, selling 3 million copies in the United States within the first two months of its release. It also marked the beginning of the Black Ops sub-series, as characters from World at War were carried over into its sequel, Call of Duty: Black Ops (2010).