The U.S. military dropped its largest non-nuclear bomb on an ISIS target in Afghanistan on Thursday.

The MOAB (Massive Ordnance Air Blast) - which is also known as the "mother of all bombs" - was deployed on a cave and tunnel system believed to be used by ISIS fighters in the Nangarhar province, very close to the Pakistan border.

It was the first time the 21,000-pound bomb has ever been used in combat.

Former intelligence officer and U.S. Army veteran Michael Pregent joined Tucker Carlson tonight to explain what this device does and why it was used today.

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Pregent explained that ISIS fighters in Afghanistan were starting to use the massive tunnel complex that Al Qaeda used starting back in 2001, when U.S. forces were deployed the country.

"They used the same tunnel complex for bin Laden to escape to Pakistan," Pregent said. "The Haqqani network, a terrorist organization out of Pakistan, uses it to bring in lethal aid. So you have these organizations like Al Qaeda, the Haqqani group, the Taliban and now ISIS using a tunnel complex to kill Americans in the past."

He said it's difficult to use precision strikes on such a complicated system of caves, canyons and tunnels, so a massive bomb like the MOAB is a much more effective option.

Pregent explained that the bomb is intended to destroy surface-level tunnels, denying our enemies the ability to use them.

He added that the devastating effects of the weapon will also make ISIS fighters think twice about using such tunnels.

Why did the Obama administration allow this complex to exist for all these years? Tucker asked.

Pregent said the MOAB is a "bravado weapon," and the past administration was focused on handing the fight off to the Afghan people and pulling Americans out.

He said that the decision to deploy the bomb sends a message to our adversaries around the world: "The next four years will be different than the last eight."

Watch more above.

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