The Mexican-American War can be defended only on the cynical grounds that it was a straight-up robbery that paid off handsomely. Other wars that were at least arguably necessary, like the Korean War, might have had vastly fewer casualties if disastrously aggressive tactics had been avoided.

The modern American debate about foreign policy could badly stand a large dose of instinctive skepticism towards the use of military force. Isolationists were wrong about the Second World War. But they were no more wrong than the so-called humanitarian interventionists were about Iraq, Libya, Somalia, or Syria in the recent past. And that ideological school of thought has not been similarly discredited despite the repeated, gruesome failure of guns and bombs to achieve anything of lasting value in the War on Terror. On the contrary, 17 years of blood has barely dented the bipartisan consensus that views U.S. military force as good by definition.