This essay is part of the special feature “Core Stories,” which commemorates the 75th anniversary of the first controlled, self-sustaining nuclear chain reaction.

On December 2, 1942, almost one year into the United States’ participation in World War II, scientists at the University of Chicago initiated the first self-sustaining nuclear chain reaction triggered by human action—the so-called Chicago Pile-1, or CP-1. Less than three years later, in August 1945, the United States became the first—and, so far, only—country to use nuclear weapons in combat, dropping them over Hiroshima and Nagasaki. The war ended in a matter of days.

In the seven decades since then, we have witnessed a brief but vigorous postwar social movement to create a world government in order to avoid nuclear war; a long, dangerous, and costly nuclear arms race between the two Cold War superpowers; and a series of nuclear crises and accidents around the world that brought us to the brink of catastrophe. At the same time, no two nuclear powers have ever fought a major war and, indeed, in the nuclear age none of the top 40 economies in the world have fought each other directly. In short, despite multiple scares and close encounters with tragedy, the nuclear age has been remarkably peaceful.

Yet, just as we prepare to commemorate the 75th anniversary of the momentous achievement by Enrico Fermi and his group in Hyde Park, the Nobel Peace Prize was awarded to a nuclear abolition advocacy group named the International Campaign to Abolish Nuclear Weapons.

How can this be? Are nuclear weapons a force for peace or, as nuclear abolitionists tell us, one of the greatest dangers for our species and our planet?

They are both. When everything goes well—when state leaders are rational, the military obeys orders, weapons systems work as planned, and each state accurately assesses the intentions of others—nuclear weapons are an unparalleled force for peace. A state that possesses, as nuclear powers do, the ability to obliterate any aggressor is highly unlikely to be attacked. This helps account for why China and other major powers have acquiesced to the United States maintaining the largest military on earth since the end of the Cold War. Their nuclear arsenals assure them that Washington will not try to come after them.

Still, nuclear weapons present grave dangers. In the hands of an irrational leader or a rogue general they can cause unprecedented destruction. Moreover, accidents happen, and therefore some argue that it is only a matter of time until a technical malfunction or human error kills millions.

Overall, maintaining nuclear arsenals entails a gamble: A bet that humans are mature, savvy, and prudent enough to possess the tools to destroy our planet and harness them in the service of peace. A bet that we can be trusted as stewards of our own destiny. So far, this bet has paid off. What can we do to ensure this continues to be the case?

First of all, we can continue to work toward limiting the size of nuclear arsenals. The lower the number of nuclear weapons on the planet, the lower the odds of an accident. Second, we can continue to work toward limiting the number of states that possess these deadliest of weapons—and to make sure those that have them implement robust command and control structures that assure their proper maintenance and avoid their unauthorized use. Finally, we must work toward ensuring that our leaders understand the need for prudence when dealing with other nuclear powers. The cardinal rule of the nuclear age is something best captured by Teddy Roosevelt’s prescient remark that when carrying a big stick, one should always speak softly.

Nuno Monteiro, AM’04, PhD’09, is director of International Security Studies and associate professor of political science at Yale University. He is the author of Theory of Unipolar Politics (Cambridge University Press, 2014) and Nuclear Politics: The Strategic Causes of Proliferation (with Alexandre Debs, Cambridge University Press, 2017).