The Systems Alliance is the representative body of Earth and all human colonies in Citadel space. Backed by Earth's most powerful nations, the Alliance has become humanity's military, exploratory, and economic spearhead.

The United Nations Space Command, more commonly known as the UNSC, is the military, exploratory, and scientific agency of the Unified Earth Government. The UNSC formed halfway through the 22nd century as remnants of old cultural ideologies clashed for supremacy in the Sol system and mainly oversaw United Nations military operations in space. The UN massively militarized its off-world colonies via propaganda and then defeated communist and fascist forces in 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 great suffering and death unto Earth and its colonies, it united humanity's militaries into a common, armed force by the end of the 22nd century.

Today, these joined factions are a force to be reckoned with.