The Subjugation of the Avatar Dimension was the conquest and enslavement of the Avatar dimension by the Galactic Empire in 10 BBY. The campaign was lead by Grand Moff Willhuff Tarkin.
Immediately after it's establishment at the end of the Clone Wars, the Galactic Empire began extending it's power over the Universe. As the Imperial war machine grew, it needed new resources. Also, the Death Star construction project was being delayed by labor shortages, supply problems, design problems, and other concerns. To solve this, the Empire began a series of campaigns, lead by Grand Moff Willhuff Tarkin, one of the most powerful Imperial officials and supervisor of the Death Star construction project, to bring natural resources, slave labor, and scientific laboratories under it's control. As a result of this, numerous species were enslaved, including the Vulcans, due to their skills in science and technology, and their laboratories, the Klingons, for their physical strength and natural resources, the Mon Calamari, for their labor and massive shipyards, and the Wookiees, for their engineering skills and physical strength.
Hopefully for the Empire, the Avatar dimension was discovered by Imperial scouts in 10 BBY. The dimension was discovered to have vast mineral resources. However, it was occupied by the Na'vi, tall blue-skinned humanoids with Native-American like culture, technology, and ways. They could also be good slave labor, while their resources could help in the Death Star's components and parts. As such, the Empire launched the subjugation of the dimension, commanded by Tarkin.
A Imperial fleet appeared over the dimension. Since the Na'vi were primitive, at a pitifully low level and at a pre-Roman state, no planetary shield or defense fleet encountered the Imperial fleet. Tarkin ordered the deployment of specially-modified AT-AT Walkers, as well stormtroopers trained to fight in forest environments. Once they deployed, however, they encountered immense resistance by the native forces, who had united to face the Imperial threat. Although the natives used small swords, bow and arrow, and spear, they knew the ways of their land, were skilled in physical combat, and were fast and agile. A large number of stormtroopers died, but Tarkin had the walkers brought out. The walkers promptly blasted away native positions, scattering them into retreat. Eventually, most of the native warriors would be exterminated.
Eventually, Imperial stormtroopers captured most of the native settlements, villages, and towns. The tribal leaders were forced to surrender, thus bringing their dimension under formal Imperial control.
The Empire promptly enslaved the Na'vi and sent in occupation forces. Many forests were leveled by Imperial walkers, and mines, refining installations, and operating facilities were established all across the mineral-rich dimension. Concentration camps and enslavement facilities were also established to contain the Na'vi. Na'vi slaves were forced to work at these installations, and some were shuttled off to work on the Death Star.