A strong Manichean streak runs through American perceptions of the outside world. That streak involves a habit of seeing all conflict and instability in binomial terms, a presumption that one of the perceived two sides is good and the other bad, and an urge to weigh in on the presumptively good side. The influence that these tendencies have had on U.S. policy has varied over time. The influence was readily apparent, for example, during the George W. Bush administration's days of “you're either with us or with the terrorists.” The Obama administration has tried to move in a less Manichean and more realist direction, especially in conducting diplomacy with Iran and in so doing opening a door to a more fruitful all-azimuths diplomacy in the Middle East generally. But the current administration still operates in a political environment in which the old perceptual habits set limits on what the administration can do, or perhaps push it into doing things it might not otherwise have done.

There have been ample demonstrations throughout the Middle East of how inaccurate and inapplicable the Manichean perspective is. There is Iraq, where the United States and the Iranian bête noire are on the same side in countering the so-called Islamic State or ISIS. There is the even more complicated deadly brawl in Syria, where the people who from the viewpoint of the West are the closest thing to good guys are opposing the same regime that also is opposed by ISIS and the local al-Qaeda affiliate.

At least as clear a lesson both in the fallacies of the Manichean perspective and the mistake of the United States taking sides in such conflicts is found in the current strife in Yemen. But the lesson does not seem to have been learned, as reflected in U.S. support for the Saudi military intervention in Yemen. Three major features of the conflict in Yemen are pertinent to that lesson.

One is that the conflict is at least as complicated and multidimensional as any others in the Middle East. It is impossible to draw a line that would put everyone worth supporting on one side and everyone worth opposing on the other, or even to come close to doing that. Al-Qaeda in the Arabian Peninsula—often considered the most capable Al-Qaeda affiliate today—is completely at odds with, and a confirmed enemy of, the Houthi forces who are the principal target of the U.S.-backed Saudi intervention. One of the most significant allies of the Houthis is Ali Abdullah Saleh, who for three decades was America's guy as ruler of Yemen.

Second, this war is, as Adam Baron has put it, “by and large, an internal Yemeni political conflict” that “remains deeply rooted in local Yemeni issues.” This fact has been obscured by those who, intent on depicting Iran as a dangerous wide-ranging regional renegade, portray the Houthi rebellion as part of some Iranian expansionist plan. It is nothing of the sort. The Houthis have been driven for years by grievances involving the distribution of resources and power within Yemen, and their more recent gains have mostly reflected the sympathy for those grievances among other Yemeni elements who have been similarly displeased and disadvantaged by the most recent Yemeni regimes.

Third, the motivations of outside actors intervening in this conflict are not ones that the United States ought to associate itself with. One set of motivations is sectarian. There is no advantage at all, and lots of disadvantage, for the United States to be seen identifying with one side or another in sectarian disputes within the Muslim world. Another set of motivations, rooted in decades of Saudi-Yemeni strife dating back to when the expansion of the Saudi kingdom first led to seizure of traditionally Yemeni provinces and to lingering border disputes, involves a Saudi desire to exercise dominance over the Arabian Peninsula and in particular this part of it. Graham Fuller observes, “Riyadh has always loathed Yemeni feistiness, independence, its revolutionary politics, and even its experiments with democracy.” The Saudis publicly play up the Iranian angle, but what they really don't like about the Houthis is that they haven't been able to buy off the Houthis as effectively as they have many other Yemeni elements. The Saudi objective of maintaining this kind of overlordship over its neighbors is also not an interest that the United States shares.

And yet the urge to take sides and intervene persists, as reflected in recent remarks about the Yemeni case by John McCain. The urge pays insufficient heed either to what is in U.S. interests or to what is effective. McCain asserted that the Saudis did not seek advance coordination with the United States concerning their intervention “because they believe we are siding with Iran.” Actually, according to a senior officer at U.S. Central Command, “The reason the Saudis didn’t inform us of their plans is because they knew we would have told them exactly what we think — that it was a bad idea.”

We know that the Obama administration is feeling the need these days to appear supportive of the Gulf Arabs because of angst related to the impending nuclear agreement with Iran. And if catering to that angst is one of the prices that has to be paid to get the agreement and, through it, to get closer to liberating U.S. diplomacy in the Middle East from rigid side-taking in the future, then this policy may turn out to be on balance worthwhile. But the Yemeni conflict itself still ought to serve as a lesson in the multiple reasons the United States would be better off to resist its side-taking urge.