Originally a colony of Earth - made up of Chinese, East Indian/Pakistani, and Texan settlers - about three generations after the first colonists dug in to the rock and soil, making Mars humanity’s second home, the colonists began to get restless. While dependent on Earth for some supplies, Mars was largely self-sustaining. It was also becoming a leader in environmental science and research as well as the design and manufacture of a new generation of spaceships.
Many of the colonists of that period wanted to secede from the rule of Earth, and compared their plight to that of North America in the 1500's (Mars was a four-month journey from Earth using the drive technology they had at the time). Two major events almost led the two planets to war, the first happened when a group of secessionists published their manifesto, leading the UN to invoke the 'breakaway province rule' and launch forty ships towards Mars. Negotiations behind the scenes eventually cooled things down, and the ships turned around and headed back to Earth.
The other major incident came when the United Nations issued a statement that all future Martian ships would be contracted through the Bush orbital shipyards on Luna. The Martian government didn't even reply to that request and work at the shipyard continued. The UN then ordered that all shipyards on Mars shut down until an inspection team could be sent out there, but it would take them seven months to get a team together, and another six to make the journey to Mars (due to the planets position at the time). Once again, this request was ignored. Rumors of war started up once again, and if not for Solomon Epstein and his accidental invention of what would come to be called the Epstein Drive, war between the planet and its colony may have been inevitable.
After Solomon invented the Epstein Drive (and lost his life on the initial test flight, due to the unprecedented power), Mars had a major technological advantage over Earth. The new ships could go further and faster than anything that had been built before, while using significantly less fuel, opening up the rest of the solar system for exploration and settlement. The colonial Martian government reached out to the UN and offered them access to the Epstein Drive in exchange for granting Mars its sovereignty.
After being granted the right to rule itself, Mars formed the Martian Congressional Republic to serve as the governing body of the people of Mars, as well as the Martian Congressional Republic Navy to serve as the military arm of the government. The Martian Congressional Republic Navy and the United Nations Navy eventually formed the Earth-Mars Coalition Navy, a joint naval war force tasked with keeping the solar system safe.
Considered by some the greatest engineering project in human history, the Mars terraforming project is the driving force of Martian society, involving most of the population of Mars either directly or indirectly.