The Islamic State and the Nusra Front have violently confronted each other for leadership of the powerful jihadist wing of the Syrian opposition to the Assad regime. Now it appears that the latter is splintering in the wake of the prestige and resources which have accrued to the Islamic State in its rapid advance across a large swathe of Syria and Iraq. The US-led air campaign, intended to halt ISIS, has instead reportedly accelerated defections from the Nusra Front to the Islamic State, and laid the basis for a merger or formal alliance of the two organizations.