PDF - http://www.brookings.edu/views/articles/byman/20051216_survival.pdf
"Open and active state sponsorship of terrorism is blessedly rare, and it has decreased since the end of the Cold War. Yet this lack of open support does not necessarily diminish the important role that states play in fostering or hindering terrorism. At times, the greatest contribution a state can make to a terrorist's cause is by not acting. A border not policed, a blind eye turned to fundraising, or even the toleration of recruitment all help terrorists build their organisations, conduct operations and survive."
