John Allen Gay sees  the recent deployment of U.S. forces to act as a buffer between Turks and Kurds as an expression of the U.S. pursuit of primacy:
Yet one could make the case that the Manbij situation, despite being condemned by many here inside the Beltway, is a logical extension, or at least a microcosm, of the bipartisan Beltway consensus on U.S. grand strategy. This grand strategy, known as primacy, suggests that the United States should take an active, leadership role in every strategically important region of the world, and that this is good for both the United States and for nations of good will in those regions.
If one accepts that the U.S. has a global “leadership” role like this, one will usually conclude that the U.S. has to police or “shape” foreign conflicts that have little or nothing to do with American security. Even when there is no discernible American interest at stake, the U.S. involves itself for the sake of exercising this supposedly necessary “leadership,” but as we can see in the case of Syria this will mean putting Americans at risk to prevent ostensible “allies” from killing each other. That calls attention to some other bad habits in our foreign policy: we extend the title of ally to a large number of groups and states, some of whom are mutually antagonistic, and then we think that it is the job of our foreign policy to satisfy all of them at the same time. That inevitably produces a confused policy that ends up satisfying no one and leaving all sides convinced that Washington is unreliable. The deployment in Syria also reminds us of the incoherence of the supposed anti-ISIS “coalition” itself. Most members of the so-called “coalition” do not consider fighting ISIS their top priority, and most have signed on to the anti-ISIS effort in the hopes of acquiring U.S. support for whatever their real goal happens to be.
As ever, the U.S. needs to be more discriminating in the fights it chooses to join and the “allies” it accepts in the process.