History of the United Nations Space Command

The United Nations Space Command (UNSC) might be the prime human government in the Halo universe. The UNSC's military arm is called the UNSCDF or the United Nations Space Command Defense Force.

Interplanetary War
The United Nations Space Command was formed as the result of a series of brutal wars across the Solar System between 2160 and 2164, most prominently among them the Jovian Moons Campaign, The Rain Forest Wars, and a series of battles on Mars. These conflicts were centered around UN clashes with dissident political movements, the most important of which were the "Koslovics" and the "Frieden." The Koslovics—supporters of neo-Communist hardliner Vladimir Koslov—sought a return to the glory days of Communism and the elimination of corporate and capitalist influence, particularly in orbital facilities and off world colonies. The Frieden movement was a resurgence of fascism, springing from anti-Koslovic sentiment that had taken root in the Jovian colonies. "Frieden" literally means "peace" - in this case, they believed that peace could be achieved only once the "oppressors on Terra Firma" were eliminated.

Lasting over four years, the massive wars raged across Earth and in numerous off-planet colonies. The brutal three-way war between UN, Koslovic, and Frieden forces sparked a massive buildup of arms and troops within the United Nations. Utilizing aggressive space-based Marine drops, the UN defeated Koslovic forces on Mars, which would pave the way for the future incorporation of Marine units as primary ground combat elements. It was at this point that the United Nations Space Command was first created to oversee UN deployments across the solar system. The UNSC proceeded to use its overwhelming military might to crush all remaining Koslovic and Frieden holdouts across the system, ending with a single Unified Earth Government.

Interstellar Colonization
Massive overpopulation and overmilitarization presented immediate problems for the postwar United Nations Space Command. Utilizing the newly developed Shaw-Fujikawa Slipspace Drive, in 2310 the UNSC deployed a vast line of colony ships to colonize the nearest planets and systems, giving birth to the "Inner Colonies." Vast numbers of citizens and soldiers travel to these new colonies, stabilizing the overpopulation problem on Earth and giving the military new tasks to handle. As the first colonists are stringently selected, the Inner Colonies eventually formed an "elite" society of the best physical and mental human specimens.

By 2490 over eight hundred worlds in the Orion arm of the Milky Way galaxy were colonized. These settlements ranged from fairly well-tamed planetary strongholds to tiny hinterland settlements. Outward expansion continued, and the Inner Colonies become a political and economic stronghold, though they relied heavily on raw materials supplied by the "Outer Colonies."

During this period, the planet Reach (orbiting Epsilon Eridani, right on Earth's metaphorical doorstep) became the UNSC's primary naval yard and training academy. Reach was a major producer of warships and colony vessels, as well as a training ground for covert operatives and Special Forces.

However, this expansion did not come without cost, as ideological and political causes resulted in many of the Outer Colonies engaging in open rebellion. A series of brushfire wars across human space sprang up, with hundreds more threatening to erupt as well. By 2517, UNSC estimates put massive, overwhelming, and uncontrollable rebellion at less than twenty years away. This resulted in the start of the Spartan-II program, to quickly and quietly deal with insurrections without incurring massive civilian casualties.

Inner Colony Wars
The UNSC participated in the Inner Colony Wars in the 2400s'. Almost nothing is known about the wars, apart that "instant, unformatted news reports caused massive civil unrest" and "almost tore down Earth's culture." It seems that the war had a major effect upon Earth and the UNSC.