CALL OF DUTY 4

The manjoirty of the games in the series have been set primarily in world War II ,with the exception of call of duty 4:Modern Warfare ,call of duty Modern warfare 2 which are set in modern times,and call of duty:Black ops which is set in the cold War era.
As of November 27,2009,total sales for the entire call of Duty series have surpassed 55 million units world wide ,taking $3 billion in retail sales in the process.

MULTI PLAYER
Call of Duty 4 features team-based and deathmatch-based multiplayer modes on various maps. Each modehas an objective that requires unique strategies to complete.^[5] Players can call in UAV reconnaissancescans, air strikes, and attack helicopters, when they achieve three-, five-, and seven-enemy kill streaks respectively.^[4] A game ends when either a team or player has reached a predefined number of points, or the allotted time expires in which case the team or player with the most points wins. If the points are even when the time expires, Sudden Death mode is activated in which there is no re-spawning and the team who either has the last man standing, or achieves the objective first are the winners. If the player is in either of the two matches, then there is an Overtime match, in which the next team to win is rewarded the victory.^[5]
The player's performance in the multiplayer mode is tracked with experience points, which can be earned by killing opposing players, completing challenges, completing objectives, or by completing a round or match. As the player gains experience, they advance in level, unlocking new weapons, perks, challenges, and gameplay modes. The highest obtainable level is 55, but on the console versions of the game, the player has the option to enter "Prestige" mode, which returns their level to one and removes all accumulated unlockables. This process can be repeated up to 10 times with a different insignia being given each time.^[6]