The first intentional U.S. air raid on civilian populations in North Korea occurred with the bombing of the capital city Pyongyang in January 1951. (YouTube video is from 1952).
Throughout the remainder of the war, a sustained U.S. air campaign targeted Pyongyang and other major cities of North Korea.
After running low on urban targets, U.S. bombers destroyed hydroelectric and irrigation dams in the later stages of the war, flooding farmland and destroying crops.
Source: Bombing of Pyongyang – Wikipedia
The U.S. dropped more bombs on North Korea than on Japanese targets in the entire Pacific theater during WWII.
Whole cities were destroyed, with many thousands of innocent civilians killed and many more left homeless and hungry.
Carpet bombing during the Korean War included 32,000 tons of napalm, often deliberately targeting civilians as well as military targets.
“Over a period of three years or so, we killed off — what — 20 percent of the population,” Air Force Gen. Curtis LeMay, head of the Strategic Air Command during the Korean War, told the Office of Air Force History in 1984.
Source: Vox