The story of "Call of Duty: Modern Warfare 2" is about an attempted invasion of the United States by Russia as retaliation for a framed massacre at the fictional Zakhaev Airport. The other plot thread of the game follows a British SAS agent and task force attempting to track down a terrorist named Makarov who is causing instability throughout the world.
The game begins with a U.S Army Ranger player character helping to train Afghan residents in the use of modern weapons and repelling an insurgent attack. This introduces the antagonist of the game, Gen. Shepherd. He holds a grudge against the rest of the world for apathy in the events of the first "Modern Warfare" game, in which a nuclear device killed 30,000 troops in Al-Asad's capital city.
To spark conflict between the United States and Russia, Shepherd arranges for a CIA agent to be found at the scene of an airport shooting staged by Makarov.
Shepherd and Makarov work together to steal a device called the ACS module, which according to the game disables the United States' satellite surveillance and allows Russia to stage a ground invasion in retaliation for the events at the airport. Shepherd believes that the invasion will kick-start a wave of military patriotism.