Mass Effect Historical Timeline

So that we can brush up on Mass Effect lore and the history that led to the events that will transpire in Mass Effect 3, UGO brings us a historical timeline that takes us through five separate eras: Pre-Council, Council, Mass Effect, Mass Effect 2, and Mass Effect 3. Let's go ahead and quote the Council Era:
20 years after the Salarians meet up with the Asari on the newly discovered Citadel, the two races form the Citadel Council. This marks the beginning of the Council Era and the Galactic Standard Timeline. The new council makes contact with the Volus and recruit them to form the Unified Banking Act. This act establishes galactic currency, linking every economy.

While all this diplomacy is going on, the Turians are in a state of civil war. The Turians were experimenting with the Mass Relays around the same time the Asari and Salarians were, expanding their empire with colonies. Eventually, the colonies became sour towards the Turian Hierarchy and wanted to branch off. After decades of fighting, the civil war finally stopped.

300 years later, the Citadel is flooded with new races and inhabitants. The Volus, Batarians, Elcor, Hanar and Quarians are granted embassies on the Citadel.

200 years after the Citadel's expansion, an exploration team opens an inactive Mass Relay leading to the Rachni homeworld, hive-minded insect-like creatures. The Rachni attack, and the Rachni Wars begin. The war rages on for 80 years before the Council finds the broken Krogan home world. They trick the Krogans into fighting against the Rachni for them. Due to the Krogans skills as warriors, the Rachni are declared extinct in a little over 200 years. As a reward, the Krogans are given an entire planet. The Krogan population explodes, causing the Citadel to form the Spectres. After an attack by the Spectres, the Krogan Rebellions begin.

100 years after the Krogan Rebellions begin, the Citadel discover the Turians who have just ended their civil war. They recruit them to fight the Krogan. Using the genophage, a Salarian weapon that infects the Krogans on a cellular level, the Turians make it so that Krogans can no longer reproduce, dooming their race for good and ending the Krogan Rebellions. As reward, the Citadel grants the Turians their own embassy.

1000 years later, the Geth Wars break out. The Quarians created machines (Geth) to help with labor, but the machines suddenly became self-aware. When the Quarians realized this and started dismantling the robots, the Geth fought back and drove the Quarians off their home world. As a result, the Quarian race became nomads and wander the galaxy as "the Migrant Fleet." As punishment for releasing the Geth on the galaxy, the Citadel Council closes the Quarian embassy.

Important Facts:

Citadel Council Formed

500 BCE: The Asari and Salarians form a galactic hub for the entire universe on the newly discovered Citadel. During this time a Turian Civil War is under way.

The Rachni Wars

1CE: In the first year marking a new era for the entire universe, war breaks out. The Rachni are discovered and they are hostile. The new Citadel Council find the Krogan and use them to defeat the Rachni.

The Founding of the Spectres

700 CE: To battle the Krogan Rebellions, the Council forms the Spectres and launches an attack.

The Genophage


800 CE: The Turians use a biological weapon on the Krogans, effectively dooming their entire race by destroying their ability to reproduce.

The Geth Uprising

1895 CE: The Quarian's machines, named the Geth, used for labor become self-aware and revolt. The Quarians are driven off their home world and become nomads.