There has been a lot of talk about humanitarian interventions over the past week, but much of it has been muddled, misleading or both. Russia has pressed for a “humanitarian mission” to the war zone in eastern Ukraine. The U.S. and its allies argue that Moscow is just using this as a pretext to invade the region. While telling Russia to back off, the Obama administration has stumbled into a new intervention of its own, launching air strikes in northern Iraq against the forces of the Islamic State, previously known as the Islamic State of Iraq and Syria (ISIS).

The humanitarian case for American action is clear. Islamic State fighters are in the midst of an avowedly genocidal campaign against the Yazidi minority in northern Iraq. ...