Halo follows the events of an inter-galactic war between the last surviving members of the human race and an advanced collection of alien races known as The Covenant. The first title in the series, Halo: Combat Evolved, was the flagship title for Microsoft's Xbox video game console when it was released in 2001. The game achieved both critical acclaim and financial success, selling more than 6 million copies worldwide. The Spartans are highly trained warriors. Although individually less powerful than the Master Chief, an army of Spartans is a lethal force. Unique to HALO 3 are the alternate armor and helmet styles worn by these soldiers.