The Blue Grass Army Depot in Kentucky on Friday worked to eliminate its cache of chemical weapons.

The process of destroying the weapons, which has gone on for more than 30 years, was expected to finish within the next few days. The weapons are destroyed through a process of neutralization, which can involve using hot water and caustic compounds to break down the chemicals in the weapon, according to the CDC.

When these weapons are neutralized, all of the world’s publicly declared chemical weapons will be no more.

Why is the U.S. destroying these weapons? After World War II, the United States built a vast chemical weapons stockpile, such as sarin nerve gas.

In 1997, it signed the Chemical Weapons Convention pledging to destroy chemical weapons. It took several more decades and cost over $40 billion to destroy the weapons. The process was lengthy because of disputed ways to safely dispose of the weapons without harming nearby communities.

This story originally appeared in WORLD. © 2023, reprinted with permission. All rights reserved.