From: The rise of the Islamic state: ISIS and the new Sunni revolution, Patrick Cockburn, Verso, 2015, pp. 94-95.
The Syrian crisis comprises five different conflicts that cross-infect and exacerbate each other. The war commenced with a genuine popular revolt against a brutal and corrupt dictatorship, but it soon became intertwined with the struggle of the Sunni against the Alawites, and that fed into the Shia-Sunni conflict in the region as a whole, with a standoff between the US, Saudi Arabia, and the Sunni states on the one side and Iran, Iraq, and the Lebanese Shia on the other. In addition to this, there is a revived cold war between Moscow and the West, exacerbated by the conflict in Libya and more recently made even worse by the crisis in the Ukraine.
The conflict has become like a Middle East version of the Thirty Years' War in Germany four hundred years ago. Too many players are fighting each other for different reasons for all of them to be satisfied by peace terms and to be willing to lay down their arms at the same time. Some still think they can win and others simply want to avoid a defeat. In Syria, as in Germany between 1618 and 1648, all sides exaggerate their own strength and imagine that temporary success on the battlefield will open the way to total victory. Many Syrians now see the outcome of their civil war resting largely with the US, Russia, Saudi Arabia, and Iran. In this, they are probably right.