There are two kinds of wars, we are told — wars of choice and wars of necessity. The former is to be avoided and the latter fought with appropriate reluctance. World War II was a good and necessary war but Vietnam was not. The war in Iraq was a matter of choice (also of imbecility) but Afghanistan was not — although it now may be. Wars can change over time. The one in Syria certainly has. It has gone from a war of choice to a war of necessity that President Obama did not choose to fight. A mountain of dead testifies to his mistake.