Fifth, arguably the most significant point, is that Islamists are united, notwithstanding the well-publicized differences between Sunnis and Shi'ites. Islamists believe the West has been weakened by cultural degradation. They also believe their goal of caliphates from Madrid to Jakarta is an inevitability. By contrast, the United States itself and its allies are divided on strategy and on the marshaling of resources to fight the enemy...
No, they are not. Shi'ia radicals and sunni radicals would just as gladly fight each other as they would non-muslims. Iran almost went to war with Taliban Afghanistan in 1998. Iran cooperated with US during OEF. AQ in Iraq is targeting shi'ias. There is regular violence in Pakistan between sunnis and shi'ias. There is little love between Iran and AQ. etc

That's like saying Pope and Falwell are same thing as both are christians trying to evangilise. Yet one is catholic and other protestant and would likely call each other heretic and infidel if given the chance.