The stargate systems are a cluster of 3 solar systems no more than a few weeks space travel from each other and the stargate portal. This meant that they were easier to colonise, being just a few weeks travel from Earth via the portal. The systems are the Halon system, the Kildae system and the Alador system.
The Halon system was first colonized in 2344, about 130 years before the events of Thunder Brigade. When Earth scientists activated the stargate portal they discovered the Halon system on the other side. Their probes revealed that L-Brus , the moon of the gas giant Ukindo-Dee , was similar in several ways to Earth and so was colonized later that year. Enora , moon of Del-Chroma was colonized next, in 2346. It was chozen because as it was an ice planet it would obivously have the right conditions for water and therefore life. The planets Arakhos and Venetrop were next to be colonized, Earth colonists were at first nervous to settle here due to the infertile soils however Arakhos became the population centre of the colonies and the capital of the Halon Empire some 100 years later. In 2347 the Kildae system was discovered just 2 weeks away from Halon. Thanks to new technologies and lessons learnt in the Halon system, Flonares and her moons, Creva and Yazz were soon colonized. Leejarna , a lava planet took some time to colonize due to the harsh conditions and it didn't establish itself as a major tourist attraction until 2350. The Alador system however was not colonized until 2465. The Earth battle fleet, sent about 15 years earlier from earth to reclaim the stargate systems stumbled upon this system just 4 weeks from Halon. They populated the worlds of Terenor and Aquarion with the large civilian population which accompanied them. These civilians were originally sent to "repopulate the stargate systems with earth-loving people". They made it easy to set up colonies on worlds which featured bearable climates and fertile soils. The Earth Alliance set up bases on the barren moons of Kelda and Kerpe I , moons of Terenor and Cali-da respectively. The system became the base of the Earth military for 4 years until they were defeated. At the end of the war, in November 2469, the United System gained control of all 3 systems.