"For the first time since the Cuban missile crisis, we have a direct threat to the use of nuclear weapons…. We have not faced the prospect of Armageddon since Kennedy and the Cuban missile crisis," U.S. President Joe Biden said in 2022.

The stark warning came after Russia's Vladimir Putin, suffering major setbacks in his full-scale invasion of Ukraine and forced to draft hundreds of thousands of civilians to bolster the military, said his government would "use all the means at our disposal" if Russia's territorial integrity was threatened.

It was not the first time he had invoked the possibility of using nuclear weapons in connection with the war in Ukraine.

"This is not a bluff," he said in a September 21, 2022, speech announcing a partial military mobilization.

Despite Putin's rhetoric, Western officials have indicated they have seen no material preparations for a nuclear strike by Russia, and some experts have pointed out that the weapons "are not that useful to achieve military objectives."

While a Russian nuclear strike on Ukraine seems unlikely, the risk of a new nuclear arms race continues to grow.

Russia and the United States have withdrawn from several key arms control treaties over the past years, with only one -- the New START treaty -- still in force and due to expire in 2026. Russia says its participation in the treaty, which limits the numbers of nuclear warheads, launchers, and bombers the two signatories can deploy, is suspended, although it has promised to abide by the limits for now.

If New START expires without a replacement, the two major nuclear powers -- for the first time since the START I treaty entered force 30 years ago, in 1994 -- will have no restrictions on how many nuclear warheads and delivery vehicles they can deploy.

The erosion of nuclear arms control treaties began in the early 2000s, when the United States withdrew from the Anti-Ballistic Missile Treaty. Signed in 1972, this was one of the first treaties -- along with the interim agreement that resulted from the first Strategic Arms Limitation Talks, or SALT I, limiting deployed warheads, from the same year -- that aimed to avoid an arms race by maintaining parity between the Soviet Union and the United States.

The ABM Treaty was designed to eliminate one of the reasons that the United States or Soviet Union would require a large arsenal: With only a limited capability to shoot down incoming missiles, there would be less need for overwhelming numbers of warheads. With the U.S. withdrawal, Russia immediately declared it would no longer abide by the limits agreed to in the START II treaty, which both powers had decided to adhere to even though the treaty had not formally entered into force.

The next major bilateral treaty to fall was the Intermediate-Range Nuclear Forces (INF) Treaty, which banned ground-launched missiles with ranges between 500 and 5,500 kilometers. The United States had long accused Russia of noncompliance with the treaty, with the Obama administration finding that a cruise missile tested by Russia in 2014 violated the treaty's range limits. The Trump administration announced that it would withdraw from the treaty in October 2018, with Russia responding in kind.

These bilateral arms control treaties brought down the number of warheads from a peak of over 60,000 when the INF treaty was signed in 1987 to less than 10,000 when New START was signed in 2011.

New Adversaries

In addition to Russia's alleged violations of the INF treaty, the Trump administration cited China's nonparticipation and the need to prepare for a potential conflict in the Southern Pacific.

China's expansion of its nuclear arsenal poses an obstacle to nuclear negotiations that did not exist during the Cold War, when non-American and Soviet arsenals -- and ambitions -- were small enough to ignore. Under U.S. President Donald Trump, the United States linked the prospects of a new nuclear agreement with Russia to the idea that China should join New START or another trilateral nuclear treaty. Last year, the Congressional Commission on the Strategic Posture of the United States found that the United States "will no longer be able to treat the Chinese nuclear threat as a 'lesser included case' of the Russian nuclear threat."

According to Stockholm International Peace Research Institute (SIPRI), China is significantly expanding its nuclear forces and may have deployed "a small number of its warheads" in 2023. It is expected to continue growing its forces over the next decade and could match American or Russian numbers of deployed intercontinental ballistic missiles in that time, although its overall number of warheads would remain lower.

Whether the world sees a massive expansion of the number of warheads stockpiled and deployed if New START is allowed to expire without a replacement remains unclear. According to Daryl Kimball, head of the Arms Control Association, the United States and Russia have more efficient ways to increase the size of their deployed arsenals. After the treaty expires, "they will both have the capacity to double the number of deployed warheads by 'uploading'," meaning increasing the number of nuclear warheads present on delivery systems that are already deployed.

Pranay Vaddi, the U.S. National Security Council's senior director for arms control, disarmament, and nonproliferation, says that while the United States must be prepared for the constraints set out in New START to "disappear without replacement," the United States does not "need to increase [its] nuclear forces to match or outnumber the combined total of [its] competitors."

Considering the United States' existing second-strike capability, it makes sense that more is not necessarily better. Just one submarine out of between eight and 10 at sea at any time carries some 100 warheads, enough to "obliterate a large country and kill many tens of millions of people," according to Kimball.

Despite the impossibility of even Russia's and China's combined nuclear forces launching a successful first strike -- one that would knock out the United States' ability to cause catastrophic damage in response -- the United States might be headed for increases in its nuclear forces.

The Strategic Posture Commission's report on preparing for threats from 2027 through 2035 states that the U.S. nuclear force must be "either larger in size, different in composition, or both" if it is to address both a revisionist Russia and a China that the report claims are "pursuing a nuclear force buildup on a scale and pace unseen since the U.S.-Soviet nuclear arms race that ended in the late 1980s."

More, More, More

The commission's report goes on to recommend that the United States urgently upload more warheads to its deployed carriers, deploy, or base nuclear forces to the Asia-Pacific theater, increase planned numbers of nuclear-capable bombers, look into fielding road-mobile nuclear missile carriers, which are not currently in the U.S. arsenal, and prepare to deploy the future Sentinel ICBM in a configuration that carries multiple independent re-entry vehicles (currently, each Minuteman III ICBM only carries one warhead, as a result of limits imposed by New START).

At the same time, Russia is also pouring resources into upgrading its arsenal, with a recent test of a new type of heavy ICBM, the RS-28 Sarmat, apparently having failed.

The Sarmat is one of six weapons that Putin unveiled at his 2018 annual address, where a video animation showed Russian missiles flying toward a target resembling Florida. Two U.S. analysts recently claimed to have found a likely deployment site for another one of Russia's nuclear-capable "invincible weapons" heralded by Putin in 2018, the Burevestnik. Russia has also raised the specter of resuming nuclear testing, preparing facilities on the island of Novaya Zemlya, where the Soviet Union tested the largest nuclear bomb ever detonated.

Putin on September 25 proposed broadening the scope of Russia's nuclear doctrine, suggesting that attacks by "nonnuclear countries with the participation or support of a nuclear country" could trigger a nuclear response, in a clear reference to Ukraine and its Western backers. The same day, China launched a nuclear-capable ICBM into the Pacific Ocean, its first ICBM test outside of its territory in over 40 years.

Besides potentially "uploading" warheads to existing carriers and developing new weapons systems, the United States recently announced it would deploy nonnuclear cruise missiles that would previously have been banned under the INF treaty to Germany, with Putin promising to respond in kind and lift a self-imposed moratorium on deploying intermediate-range missiles if the deployments go ahead.

Russia has also reportedly deployed nuclear weapons in Belarus, which had not hosted them since the early 1990s.

With numerous changes to nuclear and conventional missile force postures taking place, relations between the West and Russia and China at their lowest point since the Cold War, and with more countries building up significant stockpiles of warheads, we could already be living through the beginning of the next nuclear arms race.

And if the nuclear powers don't agree on new limits, it could be just as risky as the last one.