Nuclear umbrellas have been a central part of US nonproliferation policy for most of American nuclear history. A nuclear umbrella, also known as extended deterrence, is when one nuclear armed country, officially says it will use its nuclear weapons to protect a non-nuclear ally, i.e. the United States guaranteeing it will retaliate against North Korea if it strikes an allied country, such as Japan. The extended deterrence policy in the United States is called an extended nuclear deterrence (END) guarantee. The US began using nuclear umbrellas during the Cold War to prevent European countries from pursuing weapons programs, and have continued to be implemented up to the present day. An END guarantee can also cover conventional forces stationed in that country. It is a comprehensive way for the US to use its military power to both protect another country and avert their need to invest in military or nuclear weapons, furthering the US goal of nonproliferation.
Nonproliferation has been the main goal of the United States since World War II. Extended deterrence became a tool to reach that goal in the 1950s when the United States officially offered its nuclear umbrella to South Korea for protection against Russia. This policy ended with the end of the Cold War, as Russia was no longer the biggest nuclear threat to South Korea. However, with North Korea withdrawing from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 1994, a new threat emerged towards both South Korea, Japan, and the United States. Nuclear umbrellas were one of the only reasons many European countries did not pursue nuclear weapons, despite many countries having both the technology and resources to make a weapons program a viable defense option. More recently, this policy has been enacted in East Asia, to deter North Korea from attacking South Korea or Japan. Because of the number of countries now relying on the US nuclear program for deterrence, the US is continuously upgrading and renewing its own nuclear program.
For nuclear umbrellas to be effective, South Korea and Japan must trust that the United States would be willing to risk a counter strike from North Korea. Would the US be willing to sacrifice Washington to save Seoul? This is the key question to answer for any country that is offered extended deterrence. In the case of protection against North Korea, the general consensus is that it is. While credibility was not as certain during the Cold War era of extended nuclear deterrence, currently North Korea’s minor nuclear capabilities render it unlikely that they could launch a second strike against the United states successfully. This means the United States does have to sacrifice as much to offer South Korea and Japan extended deterrence. However, the more capability North Korea obtains, the less credible the extended deterrence will be. Increased North Korean capability would throw off the balance the United States has been able to find in the region.
