Prologue
With the conclusion of the Ori war, Earth became one of the major players in galactic politics. With the Jaffa divided into two distinct nations, the Free Jaffa Republic and the Jaffa Alliance, and the former subjects of the Ori unable to build anymore Mother Ships, Earth became more powerful then ever before.
Thanks to technology given to them by the Asgard, as well as the Ancient database in Atlantis, the people of Earth were able to create human form Replicators. Called Replins, they were programmed to be the new working class of Earth. With the conclusion of the Ori war, the Stargate was unveiled to the general public. While the governments of the world reassured their people, Earth began to change.
Atlantis remained on earth, and became the scientific center for the planet. Shipyards were built on three different planets and began to turn out at least four BC 305's every six months. The 305's were vastly superior to the 304's they were larger, faster, and equipped with the Macay Worm Drive. They were heavily armed, and used the most advanced technology of the Tau'ri, Alterans, and Asgard.
Over time the Tau'ri grew even more powerful, and they established colonies on multiple planets. They used Replins as workers, and over time created the Terran Republic. The Terran Republic was based off of the United States government, with some heavy modifications. There were four branches of the government now. The Executive Branch existed as always, however now it dealt with external politics rather than internal. The Legislative Branch, which was limited to controlling the nonmilitary budget, taxes, internal disputes and programs. The Judicial Branch still existed, and it controlled the formation of laws. The Military Branch was new, and they controlled the military and enforced Republic laws.
The Terran Republic eventually grew to encompass all of the worlds once controlled by the Ori. They also established colonies in the Ida and Ori home galaxies. By 2100, the Terran Republic controlled most of the Milky Way, all of Ida, and almost the entire Ori home galaxy named the Orion galaxy. With peace reigning throughout the Republic, and with a strong military, the Terran's returned to the Pegasus Galaxy. After a brief war with the Wraith, the Pegasus Galaxy became part of the Terran Republic.
The Republic was divided into States. Each State was a civilization that existed before the Republic. As such Earth had the largest number of States, but also the least populated. Civilizations like the Genii got one vote in the Legislative Senate, and one additional vote for every two Billion people in their State.
The Asgard, who had stored their minds in the Computer core given to the Tau'ri, were brought back thanks to hybridization technology captured from the former Wraith Michael. The Terran Republic used technology from a multitude of different sources, and over time integrated them into a cohesive unit.
The Terran Military was divided into different groups. The Terran Navy, which used ships such as Jackson class destroyers, (visualize the ship used by the Pegasus Asgard) Carter class Cruisers (visualize a very large 304 with four fighter bays) O'Neill class battleships (think Asgard Mother Ship with different weaponry) which are the only Terran Ships not to carry fighters, and Shepard class battle carriers. (Think something like Destiny except it has fighter bays all along the hull on the sides facing forward.)
The Terran Army which used infantry (armed with various energy weapons, armor, phase technology, and comprising of different species) Spider Tanks (think bloc Replicator Ship used to escape the Asgard home world only take out flight and add in two plasma cannons where spider fangs should go.) and Hover ships (think Al'kesh with two turrets on the bottom using Asgard energy weapons, and conventional bombs. Add in shields, and a modified Wraith culling beam for good measure.)
The Terran Air force used F-545's as their main fighter, (think Star Wars A-wing without lasers but add in Asgard energy weapons, drones, and a particle beam on the bottom similar to the Ancient Satellite around Atlantis in "the siege") they also used Jumpers and Jump Cruisers (think jumper with four drive pods and three times as long. It's also better armed and equipped.)
The SGC was the final branch. The SGC used SG teams, Jumpers, Tel'taks, Al'kesh, and modified Wraith Darts. The SGC was used primarily for exploration and relief aid, they were also the diplomatic front of the Republic. They were also responsible for studying new technologies and for establishing colonies. For this reason they also controlled Atlantis and Olympus class Cityships. The Olympus class city ships were the next generation of city ship. A massive saucer shape, one mile high and ten miles across, it had buildings and weapon systems on one side, and a massive energy ring along the outer edge. The ring was used for propulsion and weapons fire it also helped to reinforce the shield.
As the Terran Republic grew, peace and prosperity reigned within. More Destiny class ships were built, and the SGC began exploring hundreds of other galaxies. Thanks to the Replins, Ships, drones, ZPM's, Stargates, Cityships, and all sorts of consumer goods were easily manufactured or synthesized using the Asgard synthesizers. The Terran Republic was not limited to just humans, over time the Asgard, Jaffa, Nox, and Tolan, joined the Terran Republic.
Wars were fought occasionally, as civilizations joined the Republic, some elements tried to sabotage relations with the Republic, or in the event of joining, some civilizations broke into civil wars. These conflicts were always small and localized, rarely taking more than a year and/or a Republic battle fleet to sort out.
Some civilizations did not wish to join the Republic, and the Terrans respected that. They maintained diplomatic relations and economic trading with those civilizations, and eventually most of them joined the Republic.
That's not to say everything was perfect, fights and crimes still happened, racism and speciesism were common among smaller out of the way systems and provinces. But order and freedom was on the whole upheld. The Republic's military force was primarily used to hunt pirates, but they were more than capable of bringing together billions of ships in the event of an actual attack. The factories and shipyards of the Republic could quite easily speed up production of military goods in the event of war.
The Terrans arrived in another galaxy, they were unaware of the new and powerful enemy they were about to unleash.