“The US green belt project” is a notion that Turkish intellectuals, especially leftists, keep harping on when it comes to political Islam. What they mean by it is the US support for certain Islamist groups and regimes against the Soviet threat during the Cold War, mainly the mujahedeen who resisted the Red Army’s invasion of Afghanistan in the 1980s. In stark contrast to the negative image of today’s jihadists, the United States saw the mujahedeen as “freedom fighters” battling Soviet oppression and lent them support. ("Rambo III" is worth watching as Hollywood’s rendition of the said perception.)
That era, however, came to an end with the Soviet Union’s withdrawal and the ensuing disintegration of Afghanistan. The mujahedeen believed they on their own had led the great USSR to collapse, and some got the idea they could bring the other superpower to its knees as well. This is how the ground for al-Qaeda was laid.