At the end of the classic 1972 film The Godfather, the new don of the family, Michael Corleone, attends a baptism while his men wipe out the heads of the other New York mafia families—all of them Michael’s enemies, and all intending one day to do him harm. Rather than wait for their eventual attacks, Michael dispatched them himself. “Today, I settled all family business,” Michael says to his traitorous brother-in-law, before having him killed.Tonight, the Israelis launched a broad, sweeping attack on Iran that seems like an attempt to settle, so to speak, all family business. The Israeli government has characterized this offensive as a “preemptive” strike on Iran: “We are now in a strategic window of opportunity and close to a point of no return, and we had no choice but to take action,” an Israeli military official told reporters. Israeli spokespeople suggest that these attacks, named Operation Rising Lion, could go on for weeks.But calling this a “preemptive” strike is questionable. The Israelis, from what we know so far, are engaged in a preventive war: They are removing the source of a threat by surprise, on their own timetable and on terms they find favorable. They may be justified in doing so, but such actions carry great moral and practical risks.Preemptive attacks, in both international law and the historical traditions of war, are spoiling attacks, meant to thwart an imminent attack. In both tradition and law, this form of self-defense is perfectly defensible, similar to the principle in domestic law that when a person cocks a fist or pulls a gun, the intended victim does not need to stand there and wait to get punched or shot.Preventive attacks, however, have long been viewed in the international community as both illegal and immoral. History is full of ill-advised preventive actions, including the Spartan invasion of Athens in the 5th century B.C., the Japanese attack on Pearl Harbor, and the American war on Iraq in 2002. Sometimes, such wars are the product of hubris, miscalculation, or plain fear, but they all share the common trait that a choice was made to go to war based on a threat that was real, but not imminent.The Israelis, ironically, are in the case books as the clearest example of a legitimate preemptive attack. In 1967, Israel got the jump on an Arab coalition that had been so obvious in its march to war that it was literally broadcasting its intention to destroy Israel while its troops massed for an offensive. Indeed, international law experts have noted that the 1967 war is so clear that it is not much use as a precedent, because most enemies are not blockheaded enough to assemble an army and declare their intention to invade. (Of course, the Israelis could argue that they are already at war with Iran, a country that has launched many missiles at them and directed years of proxy attacks on their people and their military, which would be a far stronger case.)Most threats, instead, are a judgment call based on timing. What constitutes an imminent threat? The Israelis seem to have made the same judgment with respect to Iran that America made in Iraq: A regime that has expressed genocidal intent is trying to gain nuclear weapons; possession of nuclear weapons will mean, with absolute certainty, use of nuclear weapons; and therefore, waiting until the threat gels and becomes obvious is too dangerous.Such a calculation is not irrational, especially in the nuclear age, when armies no longer need to mobilize for nations to inflict ghastly damage on each other. To show infinite patience until a threat—especially a nuclear threat—becomes so obvious that the window for action shrinks to hours or minutes requires the coldest of cold blood. Few world leaders are willing to take such risks. “We no longer live in a world,” President John F. Kennedy said presciently during the Cuban Missile Crisis in 1962, “where only the actual firing of weapons represents a sufficient challenge to a nation’s security to constitute maximum peril.”But if the Israelis are setting the terms of the debate by claiming that they are embarking on a preemptive war—and not a preventive one—then they will have to make the case to the international community that the threat from the Iranian nuclear program required action now, without any further delay. Jerusalem may well be able to make this argument; if the Iranians were, as the Israelis claim, just a few weeks from assembling a small nuclear arsenal, and the ability to strike that capacity was receding from Israeli reach, then the argument for preemption is strong—especially because Iranian leaders have so often expressed their wish to wipe Israel from the map.That rationale is complicated now by the sweep and breadth of the Israeli offensive. Several senior Iranian leaders, including from the Iranian General Staff, are reportedly dead, which suggests that Israel’s goal might be decapitation of the Iranian regime, perhaps with the aim of regime change. If that is the case, then the Israelis should not box themselves in—as the Americans unwisely did in 2002—with shaky rationales about preemption. They should simply admit that they have reached a decision to end, once and for all, the existential threat to Israel from Iran.Iran’s history and its unrelenting enmity to Israel could justify such a war. A decade ago, Supreme Leader Ali Khamenei declared that the “barbaric, wolflike” and “infanticidal” Israeli regime has “no cure but to be annihilated.” The Iranians cannot now complain if the Israelis are taking them seriously; the United States has launched military actions over far weaker threats to American security. But such decisions are laden with immense danger, especially because—as the great student of armed conflict, Carl von Clausewitz, warned long ago—there is no such thing as utter finality in war. The Israeli campaign may be necessary, but so far, it seems less like a preemptive action and more like something that another philosopher of war, Michael Corleone, would easily have recognized.