Debates over foreign policy have a bad tendency to vaporize into abstract discussions of first principles: intervention or non-intervention? Responsibility to protect or mind our own business? Iraq and Syria today present a case that makes nonsense of abstractions. Intervene? The United States and its allies should intervene when intervention will advance U.S. and allied interests, consistent with U.S. and allied values. But where do we find the U.S. and allied interest in a war between al-Qaeda’s even nastier younger brother, on one side, and the mullahs of Iran on the other? If Iran were saying, “Please help us, and we’ll reorient our policy in a friendlier direction,” that would be one thing. They are not saying that. They are not doing that. They are doing the opposite.