On Sept. 12, Islamic rebels in Syria declared war … on their fellow rebels. Two Al Qaeda-linked extremist rebel groups—Al Nusrah and the Islamic State of Iraq and Al Sham, a.k.a. ISIS—followed up their declaration with an attack on the main Free Syrian Army. The two-year-old Syrian civil war is now officially a three-way fight, pitting the regime of Pres. Bashar Al Assad versus the FSA versus the Islamists.