The American atomic bombs that ended World War II 80 summers ago snuffed out tens of thousands of lives in an instant. They blighted countless others. But they also left behind a more hopeful legacy: a collective determination by world powers to avoid the use of nuclear weapons forever, and to tightly limit their possession.
Today, that achievement is coming under strain as never before.
And while that is largely down to threats from America’s nuclear-armed rivals, especially Russian President Vladimir Putin in Ukraine, there is another catalyst.
Why We Wrote This
For over half a century, almost every nation on Earth has sworn off nuclear weapons. Now some are having second thoughts, and not just because of Russian threats. U.S. allies are unsure how far Washington will go to defend them.
It is the dramatic shift in America’s relations with its closest allies that President Donald Trump has effected since his return to the White House.
The stakes are more than theoretical. Last week, cross-border attacks by India and Pakistan – nuclear-armed enemies with weapons far more powerful than the bombs that devastated the Japanese cities of Hiroshima and Nagasaki – alarmed governments worldwide by drawing perilously close to the nuclear brink.
That served as a reminder of the reason the main nuclear powers have long acted to limit these weapons’ spread, a consensus formalized in a 1970 Nuclear Non-Proliferation Treaty signed by more than 190 countries.
Once countries get nuclear arms, there’s always the danger – whether by choice or by miscalculation – that they will use them.
So far, the “club” of nuclear-armed nations has remained small: only nine of the world’s nearly 200 countries.
Yet others may soon be knocking on the door, and not only U.S. rivals like Iran.
U.S. allies in Europe and Asia have long been capable of producing nuclear arms but have chosen not to do so. Under America’s nuclear umbrella, they haven’t felt the need.
Now, international political turbulence is prompting some of them to reconsider.
Mr. Putin’s unprovoked attack on Ukraine in 2022 was the first shock.
U.S. allies in Europe were well aware that Ukraine had once had nuclear arms. When the Soviet Union unravelled, the warheads on its soil made it the world’s third-largest nuclear power. It surrendered them in return for security guarantees from the United States, Britain, and Russia itself.
The worthlessness of those guarantees threw into sharp relief the value of the nuclear deterrent that Ukraine no longer had.
Intensifying Europeans’ sense of vulnerability, Mr. Putin has also periodically threatened to use nuclear weapons in Ukraine.
Still, until recently they have trusted in the bedrock support of the U.S. as a fellow member of the transatlantic NATO alliance.
Since President Trump’s second term began, that trust has been eroding.
He has announced tariffs on the 27 countries of the European Union, describing them this week as “nastier than China.”
Initially, he cut out European NATO partners, and Ukraine, from his bid for a peace deal there, dealing directly with Mr. Putin instead.
Among Russia’s closest neighbors – Finland, the Baltic states, and Poland – there are growing doubts that Washington would stand by their side against an attack by Mr. Putin.
Hence, the impetus to rethink their nuclear policy.
Polish Prime Minister Donald Tusk, citing a “profound change of American geopolitics,” said recently, “It is time for us to look boldly” at “opportunities related to nuclear weapons.”
France and Britain, Europe’s only existing nuclear powers, have raised the idea of extending their protective nuclear umbrella to the rest of the continent.
French President Emmanuel Macron – with a domestically produced nuclear arsenal, unlike Britain’s missiles and submarines that are made in America – has suggested that Paris could protect its European allies.
The new German chancellor, Friedrich Merz, said after his party’s election victory that he wondered whether NATO would exist “in its current form” by the time of its summit next month. Since then, he has said he has been in “serious” talks on nuclear security with Mr. Macron.
Similar political winds seem to be blowing in Asia, where allies have also relied until now on the U.S. as the ultimate guarantor of their security.
They, too, have been unsettled by Mr. Trump’s tariff offensive, his dismissal of allies as freeloaders, and his reluctance to support Ukraine.
South Korea’s Foreign Minister Cho Tae-yul said earlier this year that with the “international situation developing in unpredictable directions,” the idea of acquiring nuclear weapons was “not off the table.” Polling has suggested that a sizable majority of South Koreans agree with him.
President Trump has yet to signal the sort of reinforced security commitment that might restore allies’ confidence and shore up their decision to forego nuclear arms.
Still, he does strongly favor a reduction in superpower nuclear arsenals, saying recently that their unabated modernization was a colossal waste of money.
He has also launched a high-profile effort to prevent Iran from building a nuclear weapon.
And the India-Pakistan clashes have left little doubt his administration recognizes the danger that nuclear weapons pose.
At first, Washington seemed content to let the fighting play itself out. Vice President JD Vance said the conflict was “none of our business” and that the U.S. couldn’t tell either side to “lay down their arms.”
But when India struck near the headquarters of the Pakistani unit responsible for safeguarding the country’s nuclear arms, reportedly prompting an emergency meeting of its security chiefs, the U.S. administration suddenly changed tack.
Both Mr. Vance and Secretary of State Marco Rubio contacted the warring sides. It was they who persuaded them to agree on a ceasefire.
