Why Biden and Yoon’s Agreement Is a Big Deal

The Washington Declaration signed by U.S. President Joe Biden and South Korean President Yoon Suk-yeol yesterday should be a ringing reminder of one of the greatest achievements of U.S. national security strategy: its decadeslong success in preventing the proliferation of nuclear weapons. The agreement strengthened nuclear deterrence coordination between the two allies and offered a greater sense of assurance that South Korea falls under the U.S. nuclear umbrella.

Unfortunately, the agreement’s significance will be missed by many Americans who live in what has been called the United States of Amnesia. Like so much else about the international order today, many take for granted the fact that we now live in the 78th year since nuclear weapons were used in war.

After having survived the most dangerous crisis in recorded history—the Cuban missile crisis of 1962—U.S. President John F. Kennedy predicted a world in which there would be 15 or 20 nuclear states by the 1970s. That forecast reflected the conventional wisdom of the time that as states acquired the technical and economic base to build their own nuclear weapons, many would, and the world would see recurring nuclear wars, terrorist nuclear attacks, and anarchy.

Today, however, South Korea—like most wealthy nations—does not have its own nuclear arsenal. When he met with Biden, Yoon reaffirmed his country’s Nuclear Nonproliferation Treaty commitment to remain non-nuclear and instead bet his country’s very survival on Washington’s promise to use its nuclear arsenal to deter nuclear-armed Pyongyang from attacking.

This is not because Seoul is incapable of developing its own nuclear weapons. Seven decades on, nuclear weapons are not exactly a frontier technology. Intelligence estimates indicate that North Korea, one of the world’s poorest countries, could have an arsenal of 40 nuclear weapons and a stockpile of fissile material from which it could make an additional hundred. But Pyongyang is, relatively speaking, an outlier—one of only nine countries known to have nuclear weapons.