Third Modern War
April 2031
Around the world
Regular Army victory.
  • Rebel Army fights against the Regular Army, but allies with them again when the Mars People return to conquer Earth. They escape once again.
  • Mars People are thoroughly defeated and scattered across earth. Their leader Rootmars rumouring being slain. But was lifting up from the sea and resurrected before being attack by Invaders leading up to Invaders Invasion.
Beligerants in
Regular Army
Rebel Army
Mars People

The Third Modern War takes place in Metal Slug 3.

Even though General Morden has gone into hiding since the end of the Second Modern War, the Rebel Army continues to stage conflicts across the world. Unable to resign from active duty due to their instrumental roles in stopping Morden in the past, Marco Rossi and Tarma Roving of the P.F. Squad are sent to seek and destroy all of their installations.

At the same time, the S.P.A.R.R.O.W.S. Eri Kasamoto and Fio Germi are sent to conduct an investigation of a recent string of unusual phenomenon, ranging from the disappearance of livestock and government officials to the sightings of monsters. Though it seems like none of it has any sense of reason or connection, it quickly becomes apparent that there is something greater than Morden to worry about.

Both the PF Squad and S.P.A.R.R.O.W.S. eventually meet during their investigations, and both parties ultimately join together to get to the bottom of the conflict. In addition to the Rebel Army, they are forced to fight strange creatures such as giant mutated crabs, zombified humans, and man-eating plants. After a long journey, the team finally locates General Morden, who attacks them in a reenactment of the conclusion of the First Modern War.

As Morden falls from his helicopter in defeat, everybody discovers that this "Morden" is actually one of the Mars People in disguise, and that the real Morden is again their prisoner. Realizing that the Mars People are responsible for all the strange events and kidnappings, the Regular and Rebel Armies once more join forces against the alien invaders, this time by staging an attack on their mothership. The Mars People throw their entire armada against the two armies in opposition, but are unable to stop them from destroying the mothership and rescuing Morden.

Though the PF Squad and S.P.A.R.R.O.W.S. escape the mothership, their return to Earth is challenged by Rootmars, the leader of the Mars People, as they freefall towards the ocean. After a long battle, Rootmars is destroyed and his corpse vanishes into the dark depths of the ocean. The PF Squad and S.P.A.R.R.O.W.S. manage to stay afloat until they are retrieved, while Morden and the Rebel Army once more escapes before they can be captured.