The Martian Congressional Republic is the governing body that rules over the nine billion inhabitants of Mars and is one of the two human superpowers. Their flag is reminiscent of Mars and its two moons, Phobos and Deimos.
The Republic is often in direct competition with Earth and its governing body, the United Nations. Although Mars has a significantly smaller population than Earth, the ruggedness of the people, as a result of the harsher environment and sparser resources, makes Mars a worthy counterweight to Earth's power. The Martian Congressional Republic Navy, although smaller, is considered to be more advanced.
When the Donnager is destroyed by what is believed to be OPA ships, Mars declares war on the Belt, and deploys the majority of its fleet to it. Later when Holden released information on the ships that destroyed the Donnager were actually made on Earth, United Nations Navy ships fired on Martian Congressional Republic Navy ships in Mars' orbit and destroyed the Deimos deep radar station. The MCRN then orders all their ships in the system to return to Mars and declares war on Earth.
After the protomolecule was unleashed on Eros during the Eros incident, and its existence became known to the public, the Martian fleet nuked Phoebe into a thin gas that was sucked into Saturn’s gravity.
After the Eros incident, delegates from the UN, MCR, and OPA attend a peace conference of Ceres.
In the eighteen months since the Eros incident the MCR and UN have been in the UN-MCR Cold War. When UNN and MCRN forces engage over Ganymede both Nations attend peace talks on Earth. These talks fail and the MCR enters the UN-MCR War. The war is short and after the Io Campaign it ends with a peace treaty.
With the Ring network open a huge proportion of the population of Mars begins emigrating to new worlds. With this emigration the terraforming project for Mars would never be completed. Unknown to the MCR government at this time one of its Admirals Winston Duarte had realized that Mars was economically doomed and planned to defect to a new system with a large proportion of the MCRN fleet. As part of this many more Extremist factions of the Outer Planets Alliance were contacted and supplied in secret with MCRN Frigates and equipment with which to launch a war against Mars and Earth.
During a diplomatic trip to Earth a MCRN fleet escorting the current Prime Minister Nathan Smith most of its escort moves off to engage mysterious attackers. When new escort ships arrived they expectantly attacked the Prime Minister's fleet and boarded his ship. Nathan Smith was forced to abandon the ship onboard the racing skiff Razorback on which he successfully escaped to Earth.
At this same time a third of the MCRN fleet broke off and moved towards the Sol Ring. The MCR did not know why this fleet had moved off and could not contact it. The MCR was in disarray due to this crisis and its Prime Minister off world.
With Nathan Smith on Earth the Martian government called for a vote of no confidence in him. This vote was successful and Emily Richards became the new Prime Minister. The MCR was still in a crisis and it struggled to know which of its assets it still controlled. The government was eventually stabilized by Richards and the remaining loyal MCRN forces were able to participate in the Consolidated Fleet Offensive.