Why Iran is hard to intimidate

DETERRENCE IS A simple concept: using the threat of force to stop an enemy from doing something. America ought to have no trouble restraining Iran thus. The former has a globe-striding army; the latter relies on warships and fighter jets that predate the Moon landing. In practice, though, Iran has proved devilishly difficult to deter. It is hard to put off insurgents and militias with air campaigns; their goals are attrition and survival, not well-ordered governance, and they are willing to take casualties. Full-scale invasion may be the only sure way to deter them but the history of such interventions is salutary.Since October the Islamic Republic’s in Syria and Iraq have carried out more than 160 attacks on American troops. Some were harmless—more theatre than threat—but not the one on January 28th, which killed three American soldiers at a base in north-eastern Jordan. The Houthis, meanwhile, an Iranian-backed militia in Yemen, have for months waged a campaign of missile and drone attacks against commercial ships in the Red Sea, choking off a waterway that handles perhaps 30% of global container trade.