The game is set in the same fictional world as the rest of the Halo series. Most of the game takes place in the future year 2553, over 500 years from now. In the storyline humans have developed faster than light travel, and now live on many planets and moons of the Solar System. When humanity started to build another settlement on a planet around another star they met the alien "Covenant". The Covenant declared religious war on humanity. During Halo 2 the Covenant discovered Earth. At the start of Halo 3, the Covenant are launching a full-scale invasion of Earth.
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