Call of Duty 4: Modern Warfare

"Call of Duty 4 takes place in a fictional near-future, where a radical leader has staged a coup d'état in the Middle East, and an "Ultranationalist" movement has instigated a civil war in Russia. The events of the conflicts are seen from the perspectives of an American Marine and a British SAS commando, and are set in multiple locations, including the Middle East, Azerbaijan, Russia, and Prypiat, Ukraine. The multiplayer portion of the game features various game modes, and contains a leveling system that allows the player to unlock additional weapons, weapon attachments, and camouflage schemes as they advance."

Source: Wikipedia, "Call_of_Duty_4," available under the CC-BY-SA License.