2009's Modern Warfare 2 from Infinity Ward sells 20 million copies in its first year, a record that doesn't even last a year, as Treyarch's Black Ops in 2010 goes on to sell 25 million copies in its first year. Momentum is now on Call of Duty's side, and every game is bigger than the last. World at War also packs in Zombies: a mode that started as something of a hidden extra but would soon become an increasingly pivotal mode in the franchise.

Treyarch delivers Call of Duty: World at War in 2008, a game that sells over 3 million copies in its first two months. The two-year cycle begins and continues quite successfully for a time, with Modern Warfare selling over 7 million copies in 2007 alone. Treyarch previously worked on the 2005 spinoff Call of Duty 2: Big Red One but now, the team is a mainline developer for the franchise. Eager to see these successes not skip another year, Activision brings in one of its internal studios, Treyarch, to develop Call of Duty 3 in time for a 2006 launch. Notably, there's no new game in 2004: a lone skipped year that has not happened since.Ĭall of Duty 2 is another hit, selling over 1.4 million copies and prompting Infinity Ward to start work on the 2007 entry, Call of Duty 4: Modern Warfare. In preparation for the launch of the Xbox 360, Infinity Ward grows significantly (from around 25 staff members to well over 100) and launches Call of Duty 2 in 2005.

It's a World War II shooter developed by Infinity Ward, a studio acquired by publisher Activision after the game's launch is a success. The story begins in 2003 with the first Call of Duty.

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