On July 16, 1945, a handful of scientists and military personnel watched as a fiery mushroom cloud briefly blotted out the sky over the New Mexico desert, in the first successful test of a nuclear bomb. There were tears and nervous bits of laughter in the test site control room, as everyone watched the dawn of the nuclear era.

That explosion at the Trinity test site marked the culmination of the Manhattan Project, the highly secretive U.S. government initiative aimed at beating the Nazis to developing the first nuclear bomb in history. Three weeks after that successful test, the U.S. dropped the first of two atomic bombs on Japan, which led to the end of the Second World War.

In a television interview after the Trinity explosion, scientist J. Robert Oppenheimer said people were laughing and crying at the test site bunker after the detonation. He famously said that at the time, a line from the Hindu text Bhagavad Gita ran through his head: “Now I am become Death, the destroyer of worlds.”

It’s been exactly 70 years since that first successful nuclear detonation at the Trinity test site in New Mexico, and while the world has not been destroyed, nuclear weapons remain a highly feared and much-debated threat in global politics.

Earlier this week, U.S. President Barack Obama vehemently defended a landmark nuclear deal with Iran aimed at preventing the Middle-Eastern nation from developing its own nuclear weapons. The deal will see several major world powers ease their multi-billion-dollar sanctions against Iran, in exchange for the country’s promise to scale back its nuclear program.

Obama’s U.S. critics accused him of putting Iran on the brink of becoming a nuclear power, but he insisted that negotiations are preferred over another war in the Middle East.

“Either the issue of Iran obtaining a nuclear weapon is resolved diplomatically through negotiation or it’s resolved through force, through war,” Obama said during a lengthy White House news conference on Wednesday. “Those are the options.”

The nuclear deal marked the end of more than a decade of talks between Iran and the U.S., Britain, France, Germany, Russia and China.

But despite their push for peace, those latter six nations boast considerable nuclear arsenals of their own.

Nuclear arsenals

The Cold War arms race is over, but the United States and Russia still hold more nuclear weapons than the rest of the world combined. The U.S. has an estimated 7,260 warheads in its arsenal, with 2,080 deployed at bases or with operational forces, according to a 2015 report from the Stockholm International Peace Research Institute. Russia has slightly more weapons, with about 7,500 warheads in its arsenal, including 1,780 deployed warheads.

The United Kingdom, France, China, India, Pakistan and Israel have significantly smaller arsenals, with France leading the pack at an estimated 300 warheads. Of those six countries, it’s believed only China has actively increased its weapons stockpile since last year, while the others have either maintained or slightly reduced their stores.

The only other nation with nuclear weapons is North Korea, the reclusive dictatorship that tested its first nuclear bomb in 2006. North Korea is thought to have between six and eight warheads, according to SIPRI.

SIPRI estimates there are currently about 15,850 nuclear warheads in existence, though the U.S. and Russia are actively reducing their massive stockpiles.

Building a better bomb

There have been an estimated 2,000 nuclear weapons tests since that 1945 Trinity explosion, though nuclear weapons were only ever used twice in combat, to bomb Hiroshima and Nagasaki.

Despite U.S. fears that the Germans would develop their own nuclear bomb, that never came to pass. Instead, the Americans’ Cold War rival, the Soviet Union, became the second country with a nuclear weapon after their successful test of the First Lightning bomb on Aug. 29, 1949. The Soviets and the Americans continued to test nuclear weapons throughout the early 1950s.

The U.K. became the third nation to join the world’s nuclear powers in 1952 with the successful testing of its Hurricane weapon. France achieved their first successful nuclear explosion in 1960, China tested their first fission weapon in 1964, India joined the party with the Smiling Buddha bomb in 1974 and Pakistan added its name to the mix with two successful tests in late May of 1998.

But no nation has achieved the destructive force that the Soviets unleashed on Oct. 31, 1961, when they successfully detonated the massive 50-megaton Tsar Bomba in the sky over Mityushikha Bay, an often-used Soviet test site by the Arctic Ocean. The explosion delivered more than 1,000 times the power of the Hiroshima and Nagasaki bombs combined, though no one was injured or killed in the blast.

The United Nations has been pushing for years to stop the proliferation of nuclear weapons, and to encourage existing nuclear powers to reduce their stockpiles. However, a 1996 UN agreement to ban the testing of nuclear weapons is still awaiting final signoff from the United States, China, Israel, Iran, India, Egypt, Pakistan and North Korea.

Despite not signing off on the agreement, it’s been over two decades since the last U.S. nuclear test.

Nowadays, an obelisk and plaque mark the birthplace of the atomic bomb at the old Trinity site in New Mexico.

The original Trinity explosion is shown in the video below.