Aug. 6, the anniversary of Hiroshima, should be a day of somber reflection, not only on the terrible events of that day in 1945, but also on what they revealed: that humans, in their dedicated quest to extend their capacities for destruction, had finally found a way to approach the ultimate limit.

This year’s Aug. 6 memorials have special significance. They take place shortly before the 50th anniversary of “the most dangerous moment in human history,” in the words of the historian and John F. Kennedy adviser Arthur M. Schlesinger Jr., referring to the Cuban missile crisis.

Graham Allison writes in the current issue of Foreign Affairs that Kennedy “ordered actions that he knew would increase the risk not only of conventional war but also nuclear war,” with a likelihood of perhaps 50 percent, he believed, an estimate that Allison regards as realistic.

Kennedy declared a high-level nuclear alert that authorized “NATO aircraft with Turkish pilots ... (or others) ... to take off, fly to Moscow, and drop a bomb.”

None were more shocked by the discovery of missiles in Cuba than the men in charge of the similar missiles that the U.S. had secretly deployed in Okinawa six months earlier, surely aimed at China, at a moment of elevated regional tensions.

Kennedy took Chairman Nikita Khrushchev “right to the brink of nuclear war and he looked over the edge and had no stomach for it,” according to Gen. David Burchinal, then a high-ranking official in the Pentagon planning staff. One can hardly count on such sanity forever.

Khrushchev accepted a formula that Kennedy devised, ending the crisis just short of war. The formula’s boldest element, Allison writes, was “a secret sweetener that promised the withdrawal of U.S. missiles from Turkey within six months after the crisis was resolved.” These were obsolete missiles that were being replaced by far more lethal, and invulnerable, Polaris submarines.

In brief, even at high risk of war of unimaginable destruction, it was felt necessary to reinforce the principle that U.S. has the unilateral right to deploy nuclear missiles anywhere, some aimed at China or at the borders of Russia, which had previously placed no missiles outside the USSR. Justifications of course have been offered, but I do not think they withstand analysis.

An accompanying principle is that Cuba had no right to have missiles for defense against what appeared to be an imminent U.S. invasion. The plans for Kennedy’s terrorist programs, Operation Mongoose, called for “open revolt and overthrow of the Communist regime” in October 1962, the month of the missile crisis, recognizing that “final success will require decisive U.S. military intervention.”

The terrorist operations against Cuba are commonly dismissed by U.S. commentators as insignificant CIA shenanigans. The victims, not surprisingly, see matters rather differently. We can at last hear their voices in Keith Bolender’s “Voices from the Other Side: An Oral History of Terrorism Against Cuba.”

The events of October 1962 are widely hailed as Kennedy’s finest hour. Allison offers them as “a guide for how to defuse conflicts, manage great-power relationships, and make sound decisions about foreign policy in general.” In particular, today’s conflicts with Iran and China.

Disaster was perilously close in 1962, and there has been no shortage of dangerous moments since. In 1973, in the last days of the Arab-Israeli war, Henry Kissinger called a high-level nuclear alert. India and Pakistan have come close to nuclear war. There have been innumerable cases when human intervention aborted nuclear attack only moments before launch after false reports by automated systems. There is much to think about on Aug. 6.

Allison joins many others in regarding Iran’s nuclear programs as the most severe current crisis, “an even more complex challenge for American policymakers than the Cuban missile crisis” because of the threat of Israeli bombing.

The war against Iran is already well underway, including assassination of scientists and economic pressures that have reached the level of “undeclared war,” in the judgment of the Iran specialist Gary Sick.

Great pride is taken in the sophisticated cyberwar directed against Iran. The Pentagon regards cyberwar as “an act of war” that authorizes the target “to respond using traditional military force,” The Wall Street Journal reports. With the usual exception: not when the U.S. or an ally is the perpetrator.

The Iran threat has recently been outlined by Gen. Giora Eiland, one of Israel’s top military planners, described as “one of the most ingenious and prolific thinkers the (Israeli military) has ever produced.”

Of the threats he outlines, the most credible is that “any confrontation on our borders will take place under an Iranian nuclear umbrella.” Israel might therefore be constrained in resorting to force. Eiland agrees with the Pentagon and U.S. intelligence, which also regard deterrence as the major threat that Iran poses.

The current escalation of the “undeclared war” against Iran increases the threat of accidental large-scale war. Some of the dangers were illustrated last month when a U.S. naval vessel, part of the huge deployment in the Gulf, fired on a small fishing boat, killing one Indian crew member and wounding at least three others. It would not take much to set off a major war.

One sensible way to avoid such dread consequences is to pursue “the goal of establishing in the Middle East a zone free from weapons of mass destruction and all missiles for their delivery and the objective of a global ban on chemical weapons” – the wording of Security Council resolution 687 of April 1991, which the U.S. and U.K. invoked in their effort to provide a thin legal cover for their invasion of Iraq 12 years later.

The goal has been an Arab-Iranian objective since 1974, regularly re-endorsed, and by now it has near-unanimous global support, at least formally. An international conference to consider ways to implement such a treaty may take place in December.

Progress is unlikely unless there is mass public support in the West. Failure to grasp the opportunity will, once again, lengthen the grim shadow that has darkened the world since that fateful Aug. 6.