Joseph Nye of the JFK School of Government at Harvard has an article on the concept of 'soft power' and how the US has failed to use it to fight terrorism. He also has a book on the topic.
Soft power is the ability to get what we want by attracting others rather than by threatening or paying them. It is based on our culture, our political ideals and our policies.
I've previously pointed out a Josh Marshall article for the New Yorker that touches on soft power issues. If you haven't read it yet, do so now.