U.S. destroys last of massive chemical weapons stockpile

The last of the United States' chemical weapons were destroyed at a military installation in Kentucky on Friday, President Biden announced.

Why it matters: The country's massive stockpile of deadly Cold War-era chemical warfare agents, which are banned by international law, accrued over generations and took decades and billions of dollars to dismantle.

• "For more than 30 years, the United States has worked tirelessly to eliminate our chemical weapons stockpile," Biden said, "bringing us one step closer to a world free from the horrors of chemical weapons."
• The U.S. had a self-declared deadline of Sept. 30, 2023, to eliminate the stockpile under the United Nations International Chemical Weapons Convention, which took effect in 1997.

Zoom in: The Blue Grass Army Depot in, Richmond, Kentucky — where the chemical weapons remained — completed its disposal of more than 500 tons of munitions containing mustard gas and nerve agent, the Pentagon said.

• "Chemical weapons are responsible for some of the most horrific episodes of human loss," Senate Minority Leader Mitch McConnell said Friday (R-Ky.). "Though the use of these deadly agents will always be a stain on history, today our Nation has finally fulfilled our promise to rid our arsenal of this evil."
• The Defense Department said the last munition that was destroyed was a M55 rocket filled with sarin nerve agent.

Zoom out: Chemical weapons use toxic agents to injure or kill people, and can be delivered through missiles, rockets, artillery shells, aerosol canisters, land mines, mortars and other equipment.

• The U.S. began assembling chemical weapons during World War I and continued to produce them until the late 1960s.
• It's believed the stockpile had ballooned to around 34,000 tons of material at its height, including nerve agents that disrupt the nervous system's ability to transfer messages to organs and blistering agents that severely irritate the eyes, skin, mouth and nose.
• Congress in the 1970s mandated the Defense Department and other federal agencies to eventually destroy the stockpile and outlawed the dumping of chemical weapons in the sea, which the department had previously done in Operation Chase.
• In signing the Chemical Weapons Convention in 1993, the U.S. committed to destroying its remaining chemical weapons inventory.

How it works: The weapons were stored at eight facilities in the continental U.S. and one site on Johnston Atoll in the Pacific Ocean.

• The weapons and materials were primarily destroyed in controlled environments using incineration or neutralization, a process of breaking down agents into far less harmful byproducts using hot water and other chemicals.
• Last month, a site in Colorado destroyed its final munition and is set to close.

• In total, the Pueblo Plant neutralized 2,613 tons of chemical agents in the form of more than 780,000 projectiles and mortar rounds filled with mustard gas, a blistering agent.

What they're saying: "Today—as we mark this significant milestone—we must also renew our commitment to forging a future free from chemical weapons," Biden added.

• The disposal program in total has cost the U.S. around $40 billion, according to an estimate from John Isaacs, a senior fellow at the Council for a Livable World, which advocates for the elimination of weapons of mass destruction, including nuclear weapons.
• Isaacs said the stockpile's elimination is both a monumental and concerning achievement.
• "It's an important step, and it should be marked," he said. "But the fact it took so long and was so expensive shows how difficult it is to end reliance on dangerous weapons."

The big picture: Isaacs said the U.S. should also reduce and eventually eradicate its nuclear weapons arsenal, but he also called the endeavor "a pipe dream" with China expanding its nuclear weapons, and Russia developing new delivery systems and suspending its participation in arms control treaties.

• "When peace on Earth is attained, the U.S. might get rid of its nuclear weapons," he said.

Go deeper: The U.S and Chinese militaries still aren't talking

Editor's note: This story has been updated with additional developments.