In a dramatic escalation that has sent shockwaves through the Middle East and beyond, the United States and Israel launched coordinated airstrikes on Tehran and other Iranian cities, killing Iran’s Supreme Leader Ayatollah Ali Khamenei. The strikes, carried out on Saturday, mark one of the most consequential and controversial uses of force in the region in decades. Iran has responded with retaliatory attacks against U.S. bases and Israel, raising the specter of an expanding conflict. The region now stands on a knife’s edge, and the foundations of international order face a severe test. Whatever one’s beliefs about Iran’s ruling system, this action demands sober scrutiny. The targeted killing of a sitting head of state, particularly absent clear evidence of an imminent attack, poses grave questions about legality, legitimacy and precedent. The U.S. administration has framed the strike as a preventive act to forestall Iran’s nuclear ambitions and an opportunity for the Iranian people to “reclaim” their country. Yet preventive war, invoked without indisputable proof of imme