The RDA is a quasi-governmental organisation which possesses a monopoly over all resources on any non-Earth location, a monopoly granted to the RDA by the Interplanetary Commerce Administration under the condition that the use of weapons of mass destruction of any kind be prohibited.
Activities on Pandora
Pandora, a moon in the Alpha Centauri system, was being mined by the RDA for a mineral called unobtanium, a valuable super-conductor. The mining methods employed caused serious environmental damage, which angered the Moon's native sentient race, the Na'vi, whose beliefs hold nature sacred. To deal with the Na'vi, the RDA hired mercenaries to fight them, and soon had a full military force. The scientists who came to Pandora to study its ecology in the hopes of finding a solution to restore Earth's nearly depleted ecosystem wanted to work with the Na'vi, much to the RDA's chagrin. The RDA decided to allow them to stay and created the Avatar program, to allow a selected group of scientists to operate biological bodies with both Human and Na'vi DNA.
The RDA makes their move
When scientist Tom Sully was killed in a robbery, the RDA recruited his twin brother Jake Sully, who unlike his scientist brother was a marine and paralysed from the waist down, in the hope of using him in the Avatar program as a spy to drive the Omaticya tribe of Na'vi from Hometree, their arboreal home. The RDA head of security Miles Quaritch offered to cure Jake of his paralysis in exchange for him gathering information on the Na'vi and their home, but when Parker Selfridge, the head of the company, discovered Jake trying to prevent an RDA bulldozer from destroying a Na'vi sacred site, he shut down the Avatar program and arranged for all the scientists to leave Pandora. Following this, the corporation's military forces destroyed the Omaticya's Hometree and confined the scientists to cells.
Final Battle and Defeat
After the destruction of Hometree, Jake and his allies escaped, and using his Avatar body, Jake tamed the great flying creature Toruk (one of the most sacred animals in Na'vi culture) and united many Na'vi tribes to drive the RDA off of the moon. Quaritch discovered this, and reinforced by new battalions of mercenaries, he ordered a full scale attack on the Tree of Souls, the most sacred Na'vi site in all of Pandora and the heart of its biological neural network. Destroying it would wreak great irepairable damage to the moon's ecosystem. The intial battle went well for the corporation, with their advanced weapons and superior numbers, but the tide turned when Pandora's wildlife reinforced the Na'vi and drove the RDA back to their base. Quaritch was killed in a showdown against Jake, and Selfridge along with the rest of the RDA military and staff were banished from Pandora.