The U.S. bombings that
ended World War II didn’t mark the
close of atomic warfare.They were just the beginning.

The U.S. bombings
that ended World War II
didn’t mark the close of
atomic warfare. They were
just the beginning.

From 1945 to 2017, nuclear nations
carried out more than 2,000 explosive tests
in the atmosphere, underground
and underwater, mostly in remote places.

From 1945 to 2017,
nuclear nations carried out
more than 2,000 explosive
tests in the atmosphere,
underground and underwater,
mostly in remote places.

Larger circles indicate places with many repeated tests.

Larger circles indicate places with
many repeated tests.

Some of the atmospheric tests
were magnitudes more powerful than
the bombs dropped on Japan,
sickening and displacing thousands.

Some of the atmospheric
tests were magnitudes more
powerful than the bombs
dropped on Japan, sickening
and displacing thousands.

Their descendants — who
continue to endure physical,
psychological, economic
and cultural fallout — are living
proof that nuclear weapons
should never be tested
again. If only today’s leaders
would take heed.

Their descendants — who
continue to endure physical,
psychological, economic
and cultural fallout — are living
proof that nuclear weapons
should never be tested
again. If only today’s leaders
would take heed.

About an hour’s drive from the Las Vegas Strip, deep craters pockmark the desert sand for miles in every direction. It’s here, amid the sunbaked flats, that the United States conducted 928 nuclear tests during the Cold War above and below ground. The site is mostly quiet now, and has been since 1992, when Washington halted America’s testing program.

There are growing fears this could soon change. As tensions deepen in America’s relations with Russia and China, satellite images reveal all three nations are actively expanding their nuclear testing facilities, cutting roads and digging new tunnels at long-dormant proving grounds, including in Nevada.

None of these nations have conducted a full-scale nuclear test since the 1990s. Environmental and health concerns pushed them to move the practice underground in the middle of the last century, before abandoning testing altogether at the end of the Cold War.

Each government insists it will not be the one to reverse the freeze. Russia and China have said little about the recent flurry of construction at their testing sites, but the United States emphasizes it’s merely modernizing infrastructure for subcritical tests, or underground experiments that test components of a weapon but fall short of a nuclear chain reaction.

The possibility of resuming underground nuclear testing has long loomed over the post-Cold War world. But only now do those fears seem worryingly close to being realized amid the growing animosity among the world powers, the construction at testing grounds and the development of a new generation of nuclear weapons.

As this pressure mounts, some experts fear that the United States could act first. Ernest Moniz, a physicist who oversaw the nation’s nuclear complex as energy secretary under President Barack Obama, said there’s increasing interest from members of Congress, the military and U.S. weapons laboratories to begin full-scale explosive tests once again. “Among the major nuclear powers, if there is a resumption of testing, it will be by the United States first,” Mr. Moniz said in a recent interview.

This article is part of the Opinion series At the Brink,
about the threat of nuclear weapons in an unstable world. Read the opening piece here.

This article is part of
the Opinion series At the Brink,
about the threat of nuclear
weapons in an unstable world.
Read the opening piece here.

The Trump administration privately discussed conducting an underground test in hopes of coercing Russia and China into arms control talks in 2020, and this week his former national security adviser offered a possible preview of Mr. Trump’s second term by publicly urging him to restart the nuclear testing program. The Biden administration is adamant that technological advances have made it unnecessary to resume full-scale testing, but in May it began the first in a series of subcritical tests to ensure America’s modern nuclear warheads would still work as designed. These experiments fall within the United States’ promise not to violate the testing taboo.

A return to that earlier era is certain to have costly consequences. The United States and the Soviet Union might have narrowly avoided mutual destruction, but there was a nuclear war: The blitz of testing left a wake of illness, displacement and destruction, often in remote locations where marginalized communities had no say over what happened on their own land. Millions of people living in those places — Semipalatinsk, Kazakhstan; Reggane, Algeria; Montebello, Australia; the Republic of Kiribati — became unwitting casualties to an arms race run by a handful of rich, powerful nations.

The United States detonated the first underwater nuclear weapon in the Bikini Atoll, Marshall Islands, in 1946.

Many nuclear experts believe that a single explosive test by any of the major nuclear powers could lead to a resumption of testing among them all. And while the world is unlikely to return to the Cold War spectacle of billowing mushroom clouds from tests in the earth’s atmosphere, even a resumption of underground testing, which still can emit hazardous radiation, could expose new generations to environmental and health risks.

It would open a volatile chapter in the new nuclear age as we’re still trying to understand the fallout from the first one.

The Republic of the Marshall Islands Embassy is a modest, red brick building in a leafy Washington, D.C., neighborhood. Inside, a room on the first floor is packed with cardboard boxes and filing cabinets, each brimming with U.S. government documents detailing America’s nuclear testing program in the islands. It seems like a generous collation of history — until you open a box, pick up a page and see the endless blocks of text blacked out mostly for what the government claims are national security reasons.

While the Nevada test site hosted more nuclear detonations than any other place on the planet, the United States tested its largest bombs at the Pacific Proving Grounds. The 67 nuclear weapons tested in the Marshalls from 1946 to 1958 involved blasts hundreds of times more powerful than the American bomb that demolished Hiroshima, Japan.

The potential health risks of testing were known from the start of the U.S. nuclear weapons program. Five days after J. Robert Oppenheimer’s team covertly detonated the first atomic bomb in New Mexico in July 1945, a U.S. government memorandum was drawn up describing “the........

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