It's time for the United States to hold Iran accountable.

Much has been written about the cold war between Saudi Arabia and the Islamic Republic of Iran. Though this deadly strategic competition has not caused the sweeping disorder in which the Middle East finds itself, it has widened and deepened it.

Whether in Iraq, Syria, Yemen, Afghanistan, Bahrain, Lebanon or elsewhere, the feud between Riyadh and Tehran has heightened societal divides and inflamed sectarian tensions, harming any efforts to defeat the Islamic State militant group (ISIS), end the civil war in Syria, stabilize Iraq, stop the fighting in Yemen, and solve the political crisis in Lebanon.

While both countries have always preferred to do battle by proxy—because they have more to lose than gain from a direct fight—relations have reached a boiling point, raising the possibility, for the first time in the history of their antagonistic relationship, of the cold war turning hot. This has less to do with the intensifying vitriol the Saudi and Iranian leaderships have hurled at one another recently (although that is surely of concern) and more with objective trends that go beyond sudden emotional bursts.

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