The game opens with the player and Sergeant Tarkus being deep-striked into Calderis to aid Captain Davian Thule and his initiates. As they drive away the Orks they are confronted by Mek Badzappa and his wartrukk. Although the Mek escapes, the Marines collapse the mine which they are coming through and take a victory. After this they are deep-striked from the cruiser Armegeddon into a hamlet where Scout Sergeant Cyrus is waiting for them. They manage to fight their way to the defender of the hamlet: Sergeant Avitus, and rescue him and save the hamlet from Orks. After this they receive words that Orks have attacked two more key locations and figure they must be being directed by someone. The first attack is led by a Stormboyz Nob named Skykilla and the second is being led by Warboss Gutrencha. After this the Marines obtain information from Skykillas and Gutrenchas and find that both have visited Felhammer Mine recently. They also know that Mek Badzappa is there as well. However Cyrus remains onboard the Armegeddon to provide technical support. When they enter the mine they see a Warp Spider Exarch and his retinue vanish and are rescued from Ork gunners by Sergeant Thaddeus. They also find Badzappa and his Boyz being slaughtered by an Eldar Warlock and a bunch of Guardians. Although they kill the Warlock, the Mek escapes once again. As the Warlock dies he speaks of a greater foe threatening them all but the heroes aren't that concerned.

Well there is 4 campaigns at the moment 2 German, 2 Allied. Each campaign is told from the specific faction you are currently playing as.

In an American invasion of the Middle Eastern country, a platoon from the USMC 1st Force Recon, led by Lieutenant Vasquez and Sergeant Paul Jackson, searches for Al-Asad, but only manages to secure a television station broadcasting Al-Asad's propaganda. During the final phases of the operation, United States Central Command is notified by Seal Team Six of a Russian nuclear weapon nearby, and sends the NEST to disarm it. However, the nuclear device suddenly detonates, leveling most of the city and killing everyone in the area, including most of Vasquez's crew, whose helicopter had not left the blast radius due to the last-minute rescue of a downed helicopter pilot.

The story begins in 1993 in Somalia when Elliot Salem and Tyson Rios (the protagonists of the game) are still in the U.S. 75th Ranger Regiment. They are tasked to work with Philip Clyde, a private military contractor with the Security and Strategy Corporation (SSC), to carry out an assassination. After this mission, Philip Clyde, on behalf of SSC CEO Ernest Stockwell, invites Lieutenant Colonel Richard Dalton (commander of the 75th Ranger Regiment) to join the company for a desk job. He agrees, asking to bring Salem and Rios with him as contractors, and in the following year, the three enter the private sector. Salem and Rios begin work as mercenaries. Over the course of a decade and a half, they are caught up in a complex scheme to privatize the military, and see to the plot's downfall. At the game's epilogue, we see the two protagonists start their own firm Trans World Operations, or TWO. It has also been revealed that an Army of Two movie is in the works.