In 2148 AD, humanity discovered a small cache of highly advanced alien technology buried deep beneath the surface of Mars. The creators of this technology--known as the Protheans--went extinct nearly 50,000 years ago, leaving little evidence of their existence behind. The discovery of this technology led humans to develop faster-than-light travel, allowing rapid expansion throughout the solar system.

Within a year humanity uncovered another piece of Prothean technology, a dormant mass relay that had been encased in the ice-dwarf Charon. Once activated, this relay allowed instantaneous travel across thousands of light
years to other mass relays in different parts of the galaxy. Humanity immediately began using this technology to colonize far-off star systems.
This same year, the Systems Alliance was formed by the largest governments on Earth to serve as the spearhead of humanity's expansion.

In 2157, the Alliance made first contact with an alien species known as the turians. This resulted in the First Contact War, as the next several months saw skirmishes between the turians and Earth's Systems Alliance fleets. In the largest battle of the war, the turians crushed the garrison on the human colony of Shanxi, before ultimately being driven off by the Alliance Second Fleet. This conflict drew the attention of the Citadel Council, a governing body that maintained peace and stability throughout much of the galaxy. They intervened in the conflict and brokered a peace agreement between humans and turians.

Humanity continued its rapid expansion, and in 2165 it was granted an embassy on the Citadel, the political and economic heart of the civilized galactic community. This angered another race of aliens, the batarians, who had come into competition with humanity over territory in an undeveloped region of space known as the Skyllian Verge.

Frustrated with the Council's refusal to halt human expansion, the batarians closed their embassy on the Citadel and ultimately launched a surprise attack on the human colony of Elysium. The attack failed however, and in retaliation the Alliance raided the batarian criminal base on Torfan in 2178.
Despite taking heavy losses, the Alliance soldiers utterly exterminated the inhabitants.

The year is now 2183, and the SSV Normandy--the most advanced starship ever created by the Alliance--is being put through its paces. Aboard is Commander Shepard, a talented young officer who will soon embark on a galaxy-spanning adventure with the fate of the known universe hanging in the balance...