Simplify the following text for a Grade 6 native English-speaking person.
Original: Gears of War sold over three million copies in just ten weeks and was the fastest-selling video game of 2006 , and was the second-most played game over Xbox Live during . The game has since sold over five million copies by September 2008 .
Simplified: It sold three million copies in ten weeks and was the fastest selling video game of 2006 .