Xandar was a planet located in the Tranta system of the Andromeda Galaxy. It is home to the Xandarian race and the Nova Corps - a peace-keeping police force throughout the universe.
Xandar was destroyed by the Luphomoids. The civilization would rebuild their culture as a multitude of connected spheres. Xandar would come to conflict again with the Skrull Empire in the Xandarian-Skrull War.
Xandar would be finally destroyed by the space pirate Nebula. Most all of the Xandarian people were eridicated. But the remnants of Xandar lived on. The Nova Force was placed in Richard Rider and Garthan Saal to be used to restart the Xandarian Worldmind. When they combined, Rider used the power to restart Worldmind and make Xandar once again habitable.
They would rebuild once more only to succumb to complete destruction by the Annihilation Wave in the opening salvo of the Annihilation War.
In Other Media
Xandar appears in the movie as the home of the Nova Corps. The film opens with the end of a long war between Xandar and the Kree Empire, which results in Ronan the Accuser going rogue and vowing to destroy his enemies in spite of the peace treaty. He attempts to destroy the planet using the Power Stone, but is defeated by the Guardians of the Galaxy.