Behind much of the Middle East’s chaos — the wars in Syria and Yemen, the political upheaval in Iraq and Lebanon and Bahrain — there is another conflict.

Saudi Arabia and Iran are waging a struggle for dominance that has turned much of the Middle East into their battlefield. Rather than fighting directly, they wield and in that way worsen the region’s direst problems: dictatorship, militia violence and religious extremism.

The history of their rivalry tracks — and helps to explain — the Middle East’s disintegration, particularly the Sunni-Shiite sectarianism both powers have found useful to cultivate. It is a story in which the United States has been a supporting but constant player, most recently by backing the Saudi war in Yemen, which kills hundreds of civilians. These dynamics, scholars warn, point toward a future of civil wars, divided societies and unstable governments.