Call of Duty series has been popular since its first game, and speaking of Call of Duty games, it seems that the latest game from Call of Duty series has now achieved one amazing milestone.

Call of Duty: Black Ops might be a highly controversial game due to its terrorist related content, but it's also the best-selling game in the United States according to the National Purchase Diary. In just five months, Activision has managed to sell 13.7 million copies of Black Ops across all platforms. That's a huge success for Activision and the Call of Duty franchise, but it seems that critics aren't pleased with Activision's tactics saying that Activision focuses on annual releases of their best selling franchises. According to the critics, annual releases might become boring to the fans, but 13.7 million sold copies say otherwise.

[via 1Up]