Mosul, however, represents a potentially far bigger prize, as the regional capital of the non-Kurdish section of northern Iraq. It has been a stronghold of al-Qaeda for nearly a decade, ever since militants attempted a similar takeover in late 2004, when US troops were in control. While other Iraqi cities were later largely cleared of al-Qaeda during the US troop "surge" in 2007, the group was never properly routed from Mosul, where it has since rebuilt its presence.