Islamist insurgents have been at war against the regimes of Mubarek in Egypt, and Saud in Saudi Arabia. Specifically, the Muslim Brotherhood against Mubarek, and later bin Laden's faction, which combined a lot of what was left of the Muslim Brotherhood (Zawahiri's people) with mujahadin from the Afghan-Soviet war, against the House of Saud.

The US is the active ally of both those regimes.

These insurgencies have been a feature of Islamic politics for centuries, where typically the incumbent is attacked by the out-of-power faction for having become too corrupt, too worldy, and generally not "muslim" enough.

The US just got in the middle of one of those, and got stung