Mars

Mars is home to a Predecessor site uncovered by the first team of colonists in the Valles Marineris

Following the discovery a research base was established to understand more about the site. Many years later the technology reverse-engineered from the Predecessor site enabled humanity to research medical breakthroughs, new fabrication techniques and military technologies.

However, Mars also was ground zero for an attack that nearly destroyed the Predecessor site. Dissidents who believed that the Predecessor ruins were something not to be bothered used excavation charges to severely damage the central research facility, killing hundreds of people.

Outnumbered, the facility security officers radioed to Earth regarding the situation. Especially because the non-lethal devices meant to maintain order were no longer effective because the instigators began to use the excavation equipment (such as saws, drillers) as weapons.

This situation prompted the Earth's united government to expedite the first ever extraterrestrial deployment of armed forces.

Several vehicles used to transport scientists to and from Earth to Mars were retrofitted to transport a medium-sized military force to Mars. The soldiers were handpicked from "former" military organizations such as the SAS, Delta Force and Spetsnaz.

Arriving on Mars this armed force managed to effeciently terminate the threat and those that dissented were detained and returned to Earth for interrogation and punishment.