“Why do they hate us?”

It’s a question that has bewildered Americans again and again in the wake of 9/11, in reference to the Arab and Muslim worlds. These days, however, it’s a question increasingly asked about the reclusive North Koreans.

Let’s be clear: There is no doubt that the citizens of the Democratic People’s Republic of Korea both fear and loathe the United States. Paranoia, resentment, and a crude anti-Americanism have been nurtured inside the Hermit Kingdom for decades. Children are taught to hate Americans in school while adults mark a “Struggle Against U.S. Imperialism Month” every year (it’s in June, in case you were wondering).

North Korean officials make wild threats against the United States while the regime, led by the brutal and sadistic Kim Jong-un, pumps out fake news in the form of self-serving propaganda, on an industrial scale. In the DPRK, anti-American hatred is a commodity never in short supply.

“The hate, though,” as longtime North Korea watcher Blaine Harden observed in the Washington Post, “is not all manufactured.” Some of it, he wrote, “is rooted in a fact-based narrative, one that North Korea obsessively remembers and the United States blithely forgets.”

Forgets as in the “forgotten war.” Yes, the Korean War. Remember that? The one wedged between World War II and the Vietnam War? The first “hot” war of the Cold War, which took place between 1950 and 1953, and which has since been conveniently airbrushed from most discussions and debates about the “crazy” and “insane” regime in Pyongyang? Forgotten despite the fact that this particular war isn’t even over — it was halted by an armistice agreement, not a peace treaty — and despite the fact that the conflict saw the United States engage in numerous war crimes, which, perhaps unsurprisingly, continue to shape the way North Koreans view the United States, even if the residents of the United States remain blissfully ignorant of their country’s belligerent past.

For the record, it was the North Koreans, and not the Americans or their South Korean allies, who started the war in June 1950, when they crossed the 38th Parallel and invaded the south. Nevertheless, “What hardly any Americans know or remember,” University of Chicago historian Bruce Cumings writes in his book “The Korean War: A History,” “is that we carpet-bombed the north for three years with next to no concern for civilian casualties.”

How many Americans, for example, are aware of the fact that U.S. planes dropped on the Korean peninsula more bombs — 635,000 tons — and napalm — 32,557 tons — than during the entire Pacific campaign against the Japanese during World War II?

How many Americans know that “over a period of three years or so,” to quote Air Force Gen. Curtis LeMay, head of the Strategic Air Command during the Korean War, “we killed off … 20 percent of the population”?

Twenty. Percent. For a point of comparison, the Nazis exterminated 20 percent of Poland’s pre-World War II population. According to LeMay, “We went over there and fought the war and eventually burned down every town in North Korea.”

Every. Town. More than 3 million civilians are believed to have been killed in the fighting, the vast majority of them in the north.