The SGC (Stargate Command) was originally formed as a branch of the United States Air Force in 1997. After discovering that the stargate went to multiple worlds, they were charged with assessing potential threats and exploiting the untold benefits on those worlds.
Increased international pressure led to the formation of the IOA (International Oversight Advisory). This body shaped the SGC into an international organization, and eventually an interplanetary one. While still governed by rules established under the U.S. Air Force, the SGC was no longer a direct branch of the U.S. Military.
The primary foe the SGC faced in the galaxy was the goa'uld System Lords, a group of alien parasites who inhabit the bodies of humans, controlling them utterly. The goa'uld live for many thousands of years due to a hyper-regenerative biology and advanced healing technologies. They also possess genetically encoded memories, meaning each goa'uld has all the memories, experiences, and psychoses of his race within him at birth.
Upon discovering Earth, The goa'uld found humans to be their most pleasurable hosts and enslaved our race, pretending to be gods with the power of their technology and abilities. They transplanted humans throughout the galaxy, to be slave labor and host stock for the goa'uld.
5000 years ago, humans on Earth rebelled against Ra, the leader of the goa'uld, and managed to drive him from the planet and bury the stargate. Earth, in the midst of a power struggle among the other goa'uld, was all but forgotten in their war and left to progress unmolested and unruled by goa'uld until, in the mid 1990's, the stargate was activated by a team of military and private scientists, and Ra was rediscovered on the planet of Abydos.
Nearly a decade of bloody warfare followed, with Earth fighting for survival. Now, with the aid of recovered technology that could fight the goa'uld, humans no longer saw the goa'uld as gods. The System Lords were defeated, and every last member of the ruling body of goa'uld was hunted down and exterminated.
During the second decade of the SGC, it focused on expanding Earth's influence throughout the galaxy, uniting various human and non-human cultures, building trading alliances, establishing military partnerships, and facilitating cultural exchanges. A new era of peace throughout the galaxy seemed assured.
Unfortunately, although the System Lords themselves were defeated, the goa'uld were not exterminated. A new generation of goa'uld, carrying all of the racial memories of the old System Lords, have emerged during this period of relative peace and established a foothold for themselves on long forgotten worlds untouched by the war and attrition of the previous galactic conflict. The experience of defeat has prepared the new System Lords, bent on enslaving the galaxy and reclaiming their birthright, to cope with the tactics of the SGC and the humans they call the Tau'ri.
The SGC has responded in kind, greatly expanding its presence in the galaxy, recruiting new members from around the world and throughout the galaxy, and engaging the System Lords wherever they emerge. With advanced weapons and ships based on alien technologies, the SGC is prepared to meet the System Lords on equal ground. The war is no longer one of guile against superior technology. Now it is a battle of strategy and will.
Stargate Command is sworn to the protection of Earth and humans throughout the galaxy, and their allies. They hold the line against System Lord aggression, determined to end, once and for all, slavery to the goa'uld.