Lessons for the Next War: Nuclear Weapons Still Matter

Russian President Vladimir Putin’s threats to strike Ukraine with nuclear weapons are like a flash of lightning illuminating the international chessboard. They provide a stark wake-up call to the brute fact that nuclear arsenals containing thousands of warheads remain foundational in shaping relations among great powers. While experts, commentators, and many others have been urging Washington to discount or even ignore Putin’s threats, U.S. President Joe Biden and his team know better. Claims that Ukraine lacks good targets, Russian bombs might not work, Putin’s officers could refuse to execute orders, or the risk of radiation spreading into Russia would be unacceptable are dangerous wishful thinking. Biden, CIA Director William Burns, and U.S. National Security Advisor Jake Sullivan have concluded that Putin is deadly serious. As Sullivan acknowledged last September, “We have communicated directly, privately, at very high levels to the Kremlin that any use of nuclear weapons will be met with catastrophic consequences for Russia.”

What does Biden know that makes him take Putin’s threats so seriously, and what does that tell us about any future conflict? First, Putin commands a nuclear arsenal that can literally erase the United States from the map. During the Cold War, strategists coined the acronym MAD—mutual assured destruction—to make vivid the ugly reality that a major nuclear power can destroy its adversary but doing so would trigger a retaliatory response in which the attacker would be destroyed as well. Even in the 21st century, we must still survive in a MAD world.

Second, U.S. President Ronald Reagan’s grand imperative still holds: “A nuclear war cannot be won and must never be fought.” Why is the United States not sending Americans to fight on the battlefield alongside Ukrainians? Because that would mean killing Russian troops, and as Biden has repeatedly insisted, the United States will not fight World War III for Ukraine. In considering whether and how the United States enters a future conflict—say, against China over Taiwan—U.S. presidents know that Americans’ essential national interest is the survival of their country.

Third, Putin’s nuclear arsenal includes about 1,900 tactical nuclear weapons designed for use at shorter range. With an explosive impact equivalent to the bomb the United States dropped on Hiroshima, Japan, a single weapon striking Kharkiv or Kyiv in Ukraine could match the 140,000 deaths caused by the first atomic bomb.

Fourth, as students of strategy know, nuclear weapons are a weaker power’s equalizer. During the Cold War, when NATO faced 100 Soviet divisions poised to attack West Germany and reach the English Channel in less than a week, how did the United States attempt to deter them? By deploying hundreds of tactical nuclear weapons to stop the Soviet advance—and announcing its readiness to use them. While the United States has largely phased out tactical nuclear weapons since the end of the Cold War, Russia has made them a major pillar of its security posture.

Fifth, seven decades after the first and last use of nuclear weapons in war, what is now called the “nuclear taboo” has led many to believe that nuclear weapons are no longer usable in war—despite the fact that both the United States and Russia continue to rely on the threat to use nuclear weapons to defend themselves. This is the essence of nuclear deterrence. Moreover, the United States also provides a nuclear umbrella to protect treaty allies that choose not to acquire their own nuclear weapons by guaranteeing that the U.S. arsenal will be used to defend them. Ukraine, Georgia, and Taiwan, however, have no commitment from the United States to use nuclear weapons in their defense.

Finally, it is hard to deny an uncomfortable echo of similarity between Washington’s nuclear umbrella over NATO allies and Putin’s threat of nuclear retaliation against any attack on newly annexed territory. Both cases raise questions of credibility. During the Cold War, West Germans wondered whether the United States, in responding to a Soviet invasion, would really risk Boston for Bonn. If U.S.-backed Ukrainians overrun Ukrainian territory that Putin now calls Russia, would Putin order nuclear strikes to stop them? Until it is challenged, it is difficult to distinguish between a serious threat and a bluff.

The United States is fortunate to have a seasoned Cold Warrior at its helm, applying lessons of statecraft and strategy from the defeat of the Soviet Union, recognizing the unique danger posed by nuclear weapons, thinking clearly about vital U.S. interests, and, at the same time, finding ways to meet challenges like Putin’s without stumbling into nuclear war. Russia’s war in Ukraine has taught us that the nuclear age did not end with the Cold War. As far as any eye can see, nuclear arsenals will remain a major pillar of the international security order.