Modern Warfare 2 Factions

In multiplayer these are the factions in the game:

 Task Force 141
A multinational grouping of military units or forces for the performance of a specific operation or assignment.

 US Army Rangers
The United States Army Rangers are an elite American Special Operations Force capable of conducting direct action operations.

 Op For
An opposing enemy force.

 Spetsnaz / Ultranationalists
Russian Army Special Forces, are the original Spetsnaz and are generally considered the best trained units of the Armed Forces of the Russian Federation.

Rebellion faction in Rio de Janeiro.

 Navy SEALs
The United States Navy Sea, Air, and Land Forces, commonly known as the Navy SEALs, are the Special Operations Forces of the United States Navy.

The United States Marine Corps is a branch of the United States armed forces responsible for providing force projection from the sea, using the mobility of the United States Navy to rapidly deliver combined-arms task forces.

The Special Air Service (SAS) is a special forces regiment within the British Army which has served as a model for the special forces of other countries.