Tegalus was a planet in the Milky Way galaxy which had a Stargate and was home to a race of Humans called the Tegalans. When discovered by Stargate Command in 2004, the planet was at the same level of technology as Earth in the 1950s. The planet comprised two main continents, each with their own governments; the Caledonian Federation and the Rand Protectorate. The planet was on the verge of a war for generations, which was officially declared after the arrival of SG-1. (SG1: "Icon")
In 2006, a Prior of the Ori arrived on Tegalus to help the Rand Protectorate since it was worse off than Caledonia and eventually gave them plans to construct a satellite to destroy the Caledonians, as they want nothing to do with the Ori or anything else accepted by the Rand Protectorate. SG-1 tried to stop the satellite, but the Prometheus was destroyed in the process. Dr. Daniel Jackson was eventually able to negotiate a truce where Caledonia would gain the Stargate and could use it to evacuate anyone who didn't wish to live under Ori rule.
Shortly after the Tau'ri left the planet, talks between the two countries broke down. A full-scale war ensued and both countries annihilated each other. The Stargate was presumed to have been buried in rubble. After losing contact with the planet, General Hank Landry redirected the Daedalus on its way back from Atlantis to check out Tegalus. The Daedalus found the aftermath of the war and the destroyed planet. (SG1: "Ethon")