WHEN the United States and Israel launched strikes against Iran earlier this year, the first reaction was not only on the battlefield. It was on Wall Street. Within hours of the attack, shares of America’s largest weapons manufacturers began climbing. Investors immediately understood the signal: Conflict means rising military spending, and rising military spending means profits for the companies that build the machinery of war, even push for such conflicts that kill millions of humans. This reaction was not surprising. War has long been good business for the American defense industry, the euphemism for war-weapons firms. The surge in defense...