The Milky Way, called Avalon by the Ancients (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos), is a galaxy in the Local Group. It has been home to several species influential to the history of the known universe, including the Goa'uld, the Tau'ri, and the Ancients.
Millions of years ago, the Milky Way was colonized by the Ancients. Earth, the center of the Ancient presence in the galaxy, was used as the reference point for the Stargate network, with the coordinate system inspired by constellations as seen from Earth.
Approximately five million years ago, a virulent plague infected the Ancients that nearly wiped out the species. Originating at the construction site for their new capital known as Vis Uban, the deadly disease would spread across much of the galaxy. They attempted to travel back in time, to stop the plague from spreading, but their efforts were unsuccessful. Unable to cure it, the surviving Ancients left Earth in a huge space-borne city, which they called Atlantus. 
Before leaving, the Ancients reseeded the Milky Way with human life. As a result of this intervention, the Tau'ri — the "second evolution" of the Ancients — evolved on Earth. By 9,177 BC, they developed primitive societies in isolation from the rest of the galaxy, as a result of not having access to the planet's original Stargate, which was buried under ice in the uninhabited Antarctica. This changed when the Goa'uld System Lord Ra discovered the planet and brought a second Stargate to transport Tau'ri slaves to Goa'uld-controlled planets.
By 3,000 BC, the Goa'uld had seeded the Milky Way galaxy with various Human races descendant from the Tau'ri, most prominently the Jaffa. It was at this point that the Tau'ri back on Earth rebelled against Ra, forcing him to bury his Stargate and abandon the planet.
20th century onwardsEdit
Ra's Stargate laid buried until it was unearthed in 1928 AD. In 1996 AD, the Tau'ri activated their Stargate, and their first off-world expedition to Abydos, led by Colonel Jack O'Neill, confronted and killed Ra. This event created a power vacuum in the System Lord ranks, triggering a chain of events that eventually led to the downfall of the Goa'uld as the dominant power in the Milky Way.
Following the dissolution of the System Lords, the galaxy came under siege by the old enemies of the Ancients, the Ori. A bloody crusade followed their discovery of the Milky Way, but the activation of the Ark of Truth thankfully ended it for good. With all enemies past and present defeated, the balance of power shifted to those races formerly oppressed by the others, namely the Jaffa and humans. The Der'kal Invasion marked yet another major war for the citizens of the galaxy, but the aliens were driven off at length, restoring the peace that the Tau'ri helped to win years before.
Races native to the galaxyEdit