Threaten a country or culture with a dramatic change in their way of life. The change does not have to be real. It just has to be perceived as being real. This is why good southerners fought for the evil of slavery. This is why so many good Germans and Japanese fought for evil during World War II.
This is why traditional Islam will fight long and hard. Many good Muslims will fight for many of the bad concepts present within the Koran. With the culture of hundreds of millions of lives at stake, this is why the war against terrorism just may end up becoming World War III.