In the long term, the conflict in the Middle East that is most relevant to the United States and most intimately linked to our real national interests is not Saudi vs. Iran, Sunni vs. Shia, Arab vs. Persian (or vs. Turk or Kurd) or even nationalist vs. jihadist. The conflict in the Middle East that most importantly touches long-term American interests is between modernists, liberals, and democrats on one hand and nationalists and jihadists on the other.
In the end, that is the only contest worth winning for the United States.
The old rivalry between specific nationalisms (and pan-Arab nationalism) and the universalist pretensions of Islamic radicalism grows less and less relevant daily — nationalist dictators and Islamist ideologues long ago learned how to live with one another: Ask Recep Tayyip Erdogan. From the point of view of U.S. interests, Absolutist Variety 1 and Absolutist Variety 2 will end up looking a lot alike and functioning in an effectively identical manner. Saddam Hussein and Hafez al-Assad may have looked like allies of convenience for about ten minutes inasmuch as they were socialist dictators in a more or less familiar and conventional Western mode, but that convenience was short-lived. A bomb with a relatively long fuse is preferable to a bomb with a short fuse, but it is still a bomb, and it still will need to be defused unless you want it to blow up in your face.
That’s the fundamental problem for libertarian non-interventionists and for the Trump school of “To hell with them all!” foreign policy: The United States has global interests and, hence, global vulnerabilities. There is no retreat from that fact. Even protected by our oceans, there is nowhere to run and hide for the hyperpower.