Entering a war is easy; getting out of it is the hard part. That axiom is particularly true for the United States today, as it muddles through three wars – two of which were forced upon it (Afghanistan and the “war on terror”), with the third (Iraq) started unnecessarily by a George W. Bush administration blinded by ideology and hubris.

The US has no prospect of a military victory in Afghanistan or Iraq; these wars’ economic costs can hardly be borne anymore, and political support at home is dwindling. America must withdraw, but the...