The UNSC insignia in 2557.

United Nations Space Command
Universe Halo Universe
Capital Earth
Type of Govt. Emergency Military
Military Colonial Military/United Nations Space Command
Sapience Level Sapient

The United Nations Space Command (UNSC) serves as humanity's military, exploratory and scientific agency of the Unified Earth Government. The UNSC was formed halfway through the 22nd century, a time when remnants of old cultural ideologies clashed for supremacy in the Sol System. The UNSC served mainly as an overseer of United Nations military operations in space. After initiating massive militarization propaganda throughout its off-world colonies, through the UNSC, the United Nations defeated communist and fascist forces in a conflict generally known as the "Interplanetary War" which consisted of several side-battles that took place on Mars, the Jovian Moons, and the South American rainforests. Although the Interplanetary War brought a great deal of suffering and death to both the colonial population and the residents of Earth, it also united humanity's militia forces into a common, armed force by the end of the 22nd century.

Before the Covenant attack on Harvest in 2525, Humanity was in chaos. A bloody struggle was being waged against groups of terrorists (or freedom fighters) called the Insurrectionists, who wanted independence from the Unified Earth Government. The UNSCDF, a branch of the UNSC, fought constant battles against the Insurrectionists. In an attempt to help end the long running war against the rebels, the UEG commissioned the ORION Project (also known as the SPARTAN-I project) and later the SPARTAN-II Program, which created a group of elite super-soldiers to combat the separatists and the insurrections they spawned. When the Human-Covenant war began and the technologically superior aliens began decimating the Outer colonies, these Spartans became humanity's best hope for survival. Faced with genocide on an unprecedented scale, the UNSC began mobilization for total war.

The dire circumstances of the Covenant conflict allowed the UNSC to override civilian rule and establish itself as humanity's primary government. Although the Unified Earth Government was more open to step down, the Colonial Administration, the arm of the UEG ruling over the colonies, resisted the UNSC's rise to power, and was thus stripped of its power.

By 2552 A.D., after the fall of the military fortress world Reach, Earth was the last remaining human bastion and nearly all surviving UNSC forces were committed to its defense. The Battle of Earth (Halo) saw some of the greatest bloodshed of the entire war, both in space and on the planet's surface. For several weeks, a grueling campaign of attrition, with heavy participation by surviving Spartan units, was all that stood between mankind and extinction. After a desperate struggle, the Human-Covenant war finally came to an end after a UNSC and Covenant Separatists strike force eliminated the Covenant leadership and destroyed the Flood threat.

By the time the war began, humanity had a reached Tier 3 of the Forerunner civilization ranking system. Technological improvements continued to rise due to the capture of advanced Covenant equipment, which was studied and adapted for human needs. The very best and cutting edge of UNSC war assets were supplied to the SPARTAN-II Program. Other enhancements geared towards mass production were distributed to the SPARTAN-IIIs and -IVs. One such example of war time innovation was the energy shielding adapted, and improved, for use on the MJOLNIR armor. UNSC Infinity, built near the end of the conflict, was perhaps the height of UNSC technical achievement during this troubled period. Incorporating every scrap of technical knowledge scavenged from Forerunner ruins, the Infinity stood apart as the most formidable warship and exploration vessel in human history.