This is a timeline of notable events in the galaxy before the discovery of humanity.
There may be many races who are not mentioned (such as the ones devastated by the Rachni Wars), as I do not wish to create new races.
PGE: Pre Galactic Era (ending in 500 BCE)
BCE: Before Common Era (also known as BC, Before Christ)
GE: Galactic Era (staring in 500 BCE)
CE: Common Era (also known as AD, Anno Domini)
1400 PGE (1700 BCE): Krogen civilization is crippled in a nuclear war.
200 PGE (700 BCE): Asari achieve space travel.
120 PGE (620 BCE): Asari discover FTL and begin colonizing nearby systems.
110 PGE (610 BCE): Asari discover Secondary Mass Relay in their home system.
100 PGE (600 BCE): Salarians achieve space travel.
80 PGE ( 580 BCE): Asari discover a Mass Relay Nexus and begin exploring the Relay Network.
60 PGE (560 BCE): Asari discover the Citadel, the massive space station at the center of the Relay Network.
55 PGE (555 BCE): Salarians discover prothean ruins and begin to travel beyond their home system.
45 PGE (545 BCE): Salarians discover Primary Mass Relay within their home system, and begin to explore the Relay Network.
20 PGE (520 BCE): Salarian-Asari First Contact.
0 PGE (500 BCE): Citadel Council is formed by the Asari and Salarians. Citadel Standard Calendar turns from PGE (Pre Galactic Era) to GE (Galactic Era).
25 GE (475 BCE): Rachni achieve spaceflight.
28 GE (472 BCE): Volus First Contact.
133 GE (377 BCE): Rachni discover element zero
170 GE (330 BCE): Unified Banking Act is created.
175 GE (325 BCE): Volus become the first race to gain an embassy on the Citadel, marking them as a favored race.
240 GE (260 BCE): First slower than light Rachni colony ships launch.
255 GE (245 BCE): The Terminus Wars begin as Council Space begins to bump up against the space controlled by the powers within the Terminus Systems. They are mostly low intensity conflicts.
300 GE (200 BCE): Prosperity Eternal, the first Super Dreadnought, completed by the Armali Republic.
497 GE (3 BCE): Hanar First Contact.
500 GE (0 BCE): Salarian explorers open the Relay into the Rachni's home system. They are killed by the Rachni and their ship is reverse engineered. First Rachni War begins.
505 GE (5 CE): First offensives of the 1st Rachni War begin, with several systems and even Clusters overrun by the Rachni.
512 GE (12 CE): After several years of slowing a Rachni advance, the main components of the Rachni fleet are destroyed in the 1st Battle of The Citadel. The 1st Rachni War officially ends with a lull of hostilities, but no communication with the Rachni is achieved and constant skirmishes continue.
530 GE (30 CE): The 2nd Rachni War begins with a major campaign to regain lost territory taken by the Rachni.
542 GE (42 CE): Turians achieve spaceflight.
550 GE (50 CE): The 2nd Rachni War ends, with the limited progress and mounting costs leading to most offensive operations coming to a halt.
570 GE (70 CE): The 3rd Rachni War begins with major offensives by the Rachni, overrunning vast swaths of space.
580 GE (80 CE): Krogan First Contact. Salarians begin to uplift the Krogan to be used against the Rachni.
593 GE (93 CE): Rachni territory reaches its greatest extent, containing vast swaths of what is now the Terminus Systems, Attican Traverse, and Alliance Space, while holding large amounts of Council Space.
595 GE (95 CE): The 3rd Rachni War ends with borders stabilized and the Rachni advance mostly stopped. An unsteady peace begins as conflict with the Rachni diminishes to only light border skirmishes.
622 GE (122 CE): Turians discover prothean ruins.
630 GE (130 CE): The Turian Diaspora begins, with many people leaving Palaven and colonizing distant worlds.
645 GE (145 CE): The 4th Rachni War begins with renewed offensives by the Rachni.
646 GE (146 CE): Rachni offensive is repelled and offensives into Rachni Space begin.
680 GE (180 CE): Mass Relay is discovered by the Turians, and they begin to explore and colonize beyond it.
700 GE (200 CE): Rachni have been pushed back to their home Cluster, but invasion into their home Cluster has proven to be costly. The 4th Rachni War ends with a permanent blockade of the Relay and conflict restricted to clean up of remaining Rachni forces in known space.
710 GE (210 CE): The Trebia Wars begin as the major powers within the Turian's home system begin to fight one another at a large scale. This gives the Turian independent colonies more leeway in their actions, while giving the colonies controlled by one of the Trebia powers functional independence, whether they want it or not. The Intercolonial Wars begin as the extrasolar colonies fight amongst themselves like their brethren in the home system.
720 GE (220 CE): The 5th and final Rachni War begins as the Rachni break the Council blockade and begin to push back into known space.
725 GE (225 CE): Rachni have been pushed back to their home Cluster, and the Council begins to plan for a full invasion and cleansing of remaining Rachni Space.
727 GE (227 CE): The Krogan are given an embassy on the Citadel.
730 GE (230 CE): The Hanar are given an embassy on the Citadel.
732 GE (232 CE): Operation Inferno begins with a full invasion into the Rachni home system.
740 GE (240 CE): Last known Rachni presence in their home system is eradicated.
800 GE (300 CE): The Rachni are officially declared extinct and the final Rachni War ends. Krogan begin to settle on worlds given to them by the Council.
1000 GE (500 CE): Elcor First Contact.
1022 GE (522 CE): The entirety of the Turian home system is unified into the Turian Hierarchy, which begins suppressing other cultures and replacing them with one designed by the Hierarchy. It also begins preparations for conquering the extrasolar colonies.
1040 GE (540 CE): The Unification War begins with the Hierarchy attempting to conquer all Turian colonies, to great success. Colonies that are conquered have their cultures suppressed and replaced with the highly state loyal culture of the Hierarchy.
1100 GE (600 CE): The Unification War ends with all Turian worlds under Hierarchy control and culturally unified.
1180 GE (680 CE): Several Krogan Clans and Warlords begin to fight against the other races in order to gain more land for growth. They each operate mostly independently, and sometimes fight each other. Officially, the "Krogan government" (a Council backed state with limited power), does not support any of the groups, but there is fear that its resources may be used to help them.
1193 GE (693 CE): The Office of Special Tactics and Reconnaissance (also known as SPECTER), is created by the Council.
1200 GE (700 CE): Krogan groups claim the Garden World Lusia, a planet claimed by several Asari interests. After several months of rising tensions, Specters launch attacks on Krogan infrastructure and Council fleets begin to strike at Krogan held worlds. The Krogan Rebellions begin.
1204 GE (704 CE): Turian First Contact. The Council races begin attempting to convince the Hierarchy to join in the war against the Krogan.
1206 GE (706 CE): The Volus agree to become a client race to the Turians in exchange for protection and joining the war against the Krogan. The Turian Hierarchy joins in fighting the Krogan. A Krogan warlord attacks a Turian colony and bombards it with asteroids, killing millions. This does not have the expected reaction, increasing the Turian people's resolve to defeat the Krogan.
1220 GE (720 CE): The genophage is created by the STG and deployed by the Hierarchy, sterilizing much of the Krogan population and restricting their ability to replenish their numbers.
1240 GE (740 CE): The Krogan begin to feel the effects of the genophage on their ability to replace troops (though the cultural, moral, and economic effects were already long engrained).
1281 GE (781 CE): The Siege of Tuckunka begins, a protracted attack on the Krogan homeworld and system by the Council races.
1305 GE (805 CE): The Siege of Tuchanka ends with the world captured by the Council races. This does not end Krogan resistance and the war continues, though with the Krogan having limited ability to replace materials, munitions, and equipment due to the capture of several of their industrial centers.
1358 GE (858 CE): The Krogan Rebellions officially end, though resistance and fighting
continues in large amounts for several decades and some resistance groups continue existing for centuries or even milenia to come.
1360 GE (860 CE): The Treaty of Farixen is created, limiting the number of Dreadnoughts any race can have. The Citadel Conventions are also created.
1371 GE (871 CE): The STG escalates its efforts to destabilize the Terminus Systems, a collection of civilizations that grew prosperous while the Council races were fighting the Krogan Rebellions.
1381 GE (881 CE): The Elcor gain an embassy on the Citadel.
1403 GE (903 CE): The holo film Burning Skies of Tharisu premieres across the galaxy. The war drama about the real events of the Siege of Tharisu during the final years of the 3rd Rachni War receives universal acclaim and will hold the title of largest grossing film for over a millennium, not surpassed until The Flames of Palavin, which premieres in 2208.
1410 GE (910 CE): The Great Terminus War begins, the efforts of the STG to destabilize the region having born fruit and, after several decades of rising tensions, conflict, and numerous "tragedies" and assassinations, the majority of the Terminus Systems fall into numerous concurrent and massive wars, called the Great Terminus War.
1480 GE (980 CE): The Great Terminus War ends, turning the Terminus Systems from a growing region closing in on prosperity of Council Space, into a divided, dangerous, and economically devastated area. Clusters and systems once firmly in the hands of terminus powers begin to be developed and controlled by interests from Council Space.
1600 GE (1100 CE): Information of the STG disruption efforts and part in the start of the Great Terminus War is leaked to the public, causing massive negative reactions and an animosity from the people of the Terminus to the Council races that has not been erased even over a millennium afterwards is created. The 1st Terminus Crusade begins in reaction to this revelation, an attack by multiple united Terminus powers against the Council races' interests and space.
1612 GE (1112 CE): The 1st Terminus Crusade ends with a large loss of life and economic damage.
1680 GE (1180 CE): Vorcha First Contact. They begin to be transported off their homeworld by accident and to be used as troops.
1740 GE (1240 CE): The expansion of interests from Council Space into the Terminus Systems begins to increase as the fallout of the 1st Terminus Crusade dissipates.
1815 GE (1315 CE): The 2rd Terminus Crusade is launched in response to the increase in intrusion into the Terminus Systems by the Citadel races.
1820 GE (1320 CE): The 2nd Terminus Crusade ends, proving to have been less successful then its predecessor, but still damaging the economies of Citadel Space and halting most encroachment into the Terminus Systems.
1900 GE (1400 CE): Extensive and unchecked industrial expansion on the Drell homeworld begins to take its toll
1915 GE (1415 CE): A resurgence in Krogan hostility begins across Citadel Space, funded by Terminus powers. Most remaining Krogan warbands from the Rebellions join up in what is sometimes known as the 2nd Krogan Rebellion alongside a number of pirates, bandit kings, and younger Krogan.
1917 GE (1417 CE): The main military force of the resurgence is defeated, but the event increases galactic concerns over the Krogan.
1971 GE (1471 CE): The Galactic Calendar Standardization Act creates the modern calendar, with the founding of the Citadel Council made year zero.
2000 GE (1500 CE): Addendum is added to the Treaty of Farixen, restricting the total tonnage of Cruisers over roughly 920 thousand tons a race is allowed to have.
2078 GE (1578 CE): The STG begins to regularly update the genophage in order to keep Krogan population growth limited.
2094 GE (1594 CE): Quarian First Contact. Despite their location close to the Terminus Systems, the Quarians hold stronger connections to the Citadel races due to close Relay connections and other factors.
2100 GE (1600 CE): The Collectors are first sighted within the Terminus Systems.
2125 GE (1625 CE): Deal is brokered between the Council and the Quarians, allowing Quarian Space to be used as a jumping off point for development and colonization of the far side of the Terminus Systems, creating a new age of expansion into the Terminus Systems. The area near to Quarian Space within the Terminus Systems becomes known as the Expansion Region as a result.
2200 GE (1700 CE): The 3rd Terminus Crusade is launched in response to Citadel race encroachment into the Terminus Systems. The main battleground is the new colonies and Quarian Space.
2209 GE (1709 CE): The 3rd Terminus Crusade ends with significant economic damage being wrought upon Citadel Space, especially the Quarians, who will take until 1781 to fully recover.
2333 GE (1833 CE): The Geth are created by the Quarians, leading to great economic growth and an increase in encroachment into the Terminus Systems, the greatest yet, with massive amounts of investments being funneled into both the Quarian economy and the new territories.
2350 GE (1850 CE): Turian colonial expedition launches from the Cyclops Delta into the depths of space. Later in the year it would find and settle the world to be known as Baikonur. The colony ships are dismantled to build the settlement, the colonists not wishing to interact with the rest of the galaxy.
2351 GE (1851 CE): Turian colony on Baikonur is beset by infighting, leading to the destruction of much of the colony's advanced equipment. Infighting intensifies over the remaining equipment.
2355 GE (1855 CE): Turian population of Baikonur drops below 600 people, the number needed for a sustainable Turian population. Fighting continues among the remaining Turians,now more for resources than the original disputes that started the conflict.
2380 GE (1880 CE): Aria T'loak arrives on Omega.
2395 GE (1895 CE): The Geth gain sentience and the Quarians attempt to kill them, thus starting the Morning War (or the Geth-Quarian War). The 4th Terminus Crusade begins only months later, the Terminus powers taking advantage of the war while also distracting the Citadel races from responding to the events in Quarian Space, the many years of peace having weakened the power of the Citadel militaries.
2396 GE (1896 CE): The Morning War ends with the Quarians driven to near extinction and their core space taken over by the Geth, though several once Quarian Clusters remain contested or entirely in organic control. The increased difficulty in traveling to the Expansion Region caused by the rise of the Geth greatly hampers the war effort of the Citadel militaries. Nonetheless, the fierce fighting in the region continues.
2400 GE (1900 CE): The Destiny Ascension begins construction.
2414 GE (1914 CE): The 4th Terminus Crusade ends as the most devastating yet, with the entirety of the Expansion Region lost to the Terminus or abandoned while Citadel Space itself faces a major economic depression that will last decades known as the Black Years. Much of the anger over the event is directed at the Quarians, partially due to their responsibility in the event and partially due to other groups fanning those flames to avoid the rage being directed at them.
2420 GE (1920 CE): Last Turian on Baikonur (the grandchild of an original colonist) dies.
2450 GE (1950 CE): The Destiny Ascension is completed, work on it having been slowed by the Black Years.
2455 GE (1955 CE): The Black Years end as Citadel Space mostly recovers from the depression, however expansion still remains minimal, the scar of the 4th Terminus Crusade remaining in people's minds.
2457 GE (1957 CE): Humanity archives spaceflight.
2460 GE (1960 CE): Aria T'loak takes over Omega.
2483 GE (1983 CE): Drell First Contact. The Hanar begin attempting to rescue Drell from their devastated homeworld.
2485 GE (1985 CE): The 2nd Great Terminus War begins due to STG disruption, causing great chaos.
2500 GE (2000 CE): Expansion begins again as the Terminus powers are distracted by the war.
2524 GE (2024 CE): The 2nd Great Terminus War ends, but the conflict left the Terminus powers too devastated to do anything about the Citadel races' expansion.
2585 GE (2085 CE): Batarian First Contact.
2625 GE (2125 CE): Yahg First Contact. The Yahg homeworld is declared off limits after the Citadel ambassadors are killed by the hostile race.
2630 GE (2130 CE): The 5th Terminus Crusade begins.
2638 GE (2142 CE): The 5th Terminus Crusade ends with major damage being done to Citadel Space both economically and physically as Terminus raiding fleets roamed across all of Citadel Space.
2648 GE (2148 CE): Humanity discovers prothean ruins and begins to explore beyond its home system.
2649 GE (2149 CE): Humanity discovers the Charon Relay and begins to explore beyond it.
2657 GE (2157 CE): Human First Contact. The First Contact War begins.
