Timeline

This is the timeline of the Mass Effect universe.

48000 BCE (Approximate)
The protheans, who were a galaxy-wide civilzation linked by the mass relay network, mysteriously vanished, leaving only ruins. Much of the technology in use by younger species such as humans is based on their artifacts. Archeologists speculate that they were destroyed.

1900 BCE (Approximate)
Tuchanka, the krogan homeworld, enters the nuclear age. In a global conflict, weapons of mass destruction are released, triggering a nuclear winter. In the resulting chaos, krogan society devolves into a collection of warring clans.

900 BCE (Approximate)
After developing faster-than-light spacefaring capabilities based upon prothean technology, the asari begin to map the mass relay network, and discover the huge Citadel space station, followed shortly by the salarians.

They together colonize the Citadel station and establish a galactic community, led by the Citadel Council. With the participation of the volus, a single galactic currency is established, linking all economies.

The Rachni War
The rachni are discovered when an expidition opens a dormant mass relay to their star systems. They prove to be hostile and begin a war with the rest of the galaxy. The salarians transplant the primitive krogan to another world and manipulate them into acting as soldiers for the Citadel Council; the krogan eradicate the rachni. Free of the harsh environment of their homeworld, the krogan population explodes.

The Krogan Rebellions
Krogan warlords leverage veterans of the Rachni Wars to annex territory from others in council space. Eventually the council demands withdrawl from an asari colony, but the krogans refuse. A pre-emptive strike is made on krogan infrastructure by the council. The war known as the Krogan Rebellions occur.

First contact is made with the turians. In response to krogan threats, they declare war. After the krogan devestate turian colonies with weapons of mass destruction, the turians defeat the krogan using a salarian engineered bioweapon, known as the genophage. The krogan population starts its decline.

The turians are granted a place on the Citadel Council, and their fleet acts as galactic peacekeeper.

The Geth War
The quarians create the geth. The geth rebel against their quarian masters and reduce the quarians to a species of spacefaring nomads. They do not venture out of their systems to make war on organic species as was expected.

2148 CE
Humanity discovers a small cache of highly advanced prothean technology hidden deep beneath the surface of Mars. Building on the remnants of this long extinct race, humanity quickly masters the science of mass effect fields, leading to the development of faster than light travel.

2149 CE
Spreading out through their own solar system, humanity discovers that Charon, Pluto's moon, is actually a massive piece of dormant prothean technology - a mass relay - encased in ice.

Once activated, humanity discovers that the mass relay allows instantaneous travel across thousands of light-years to a synchronized mass relay in another part of the galaxy.

There they discover several more relays that are dormant. Over the next decade, humanity expands rapidly, establishing colonies and activating dormant relays to open up more and more unexplored regions of space.

2155 CE
To defend its rapidly expanding empire, humanity assembles a massive fleet and constructs an enormous military space station at the nexus of several key mass relays... even though they have yet to encounter another intelligent space-faring species.

The First Contact War
Humanity makes first contact with another space-faring culture: the turians. Unfortunately, the encounter is far from peaceful. The turians find the human fleet attempting to activate a mass relay, something forbidden in galactic law after the Rachni Wars, and attack. Over the next several months, a brief but tense conflict known on Earth as the First Contact War ensues.

This conflict draws the attention of the Citadel Council. The Council intervenes before hostilities escalate further, revealing the existence of the greater galactic community to humanity and brokering a peace between them and the turians.

2165 CE
Humanity continues to expand, founding more colonies and establishing trade alliances with many of the other species who recognize the authority of the Citadel Council. In 2165, the Council makes official recognition of humanity's growing power and influence in the galactic community. Humanity is granted an embassy on the Citadel, the political and economic heart of the galaxy. The events of Mass Effect: Revelation occur.

2183 CE
Commander Shepard - a promising young officer in the human Systems Alliance Military - is assigned to the crew of the prototype SSV Normandy, the most advanced vessel yet designed.