Call of Duty: World at War is a first-person shooter video game developed by Treyarch and published by Activision for Microsoft Windows, Nintendo DS, PlayStation 2, PlayStation 3, Wii, and Xbox 360. It is the fifth installment in the Call of Duty series excluding expansion packs. The game's setting returns to World War II, after the previous title Modern Warfare's modern settings. It focuses on the Pacific Theater and Eastern Front of World War II in the Microsoft Windows, PS3, Wii and Xbox 360 version. The title, game details and estimated release date were announced on June 23 2008 and the game was released worldwide between November 11, 2008 and November 14, 2008. A Windows Mobile version was also made available by Glu Mobile and different storyline versions for the PS2 and Nintendo DS were made, but remain in the World War II setting. The game uses an enhanced version of the Modern Warfare's game engine with increased development in audio effects. The story for the PC, PS3, Wii and Xbox 360 focuses on the initial battles of World War II in the Pacific and Eastern Europe involving the United States, the Empire of Japan, the Soviet Union, and Nazi Germany. It is told from the perspectives of a Marine Raider and a Red Army soldier and is based on several historical battles, including the raid on Makin Island, the Battle of Stalingrad, the Battle of Peleliu, the Battle of Seelow Heights, the Battle of Okinawa, and the Battle of Berlin. The multiplayer portion of the game contains various game modes and a leveling system that allows the player to unlock additional weapons and rewards as they progress, which was originally implemented in Call of Duty 4: Modern Warfare. A new feature to the Call of Duty series is the cooperative mode, which can support up to four players online and two offline.