I was a bad pupil. Showed up late. Left early. Forgot my textbook. Barely spoke.

Fortunately, this was no ordinary class. There were no grades. And I was there merely to observe congressman Mike Gallagher (R., Wis.) and Aaron MacLean of the Foundation for Defense of Democracies lead 20 students in a week-long Hertog Foundation seminar on the Korean war.

The strife began on June 25, 1950, when the Communist Democratic People’s Republic of Korea suddenly invaded the American-aligned Republic of Korea. An underequipped and ill-trained U.S. force was caught by surprise. The subsequent intervention, dubbed a “police action” and conducted under the auspices of the United Nations, lasted from 1950 to 1953. The combatants agreed to an armistice 70 years ago this week.

More than 36,000 U.S. servicemen — and hundreds of thousands of South Koreans — were killed in action. The whereabouts of some 7,000 of our soldiers remain unknown. And around 30,000 American personnel remain stationed in the Republic of Korea, where they guard the 38th Parallel that divides the free people of the south from the nuclear-armed enslavers in the north.

Korea was the first sign that the Cold War between the United States and the Soviet Union would be hot indeed. This “Forgotten War,” sandwiched between World War II and Vietnam, holds cautionary lessons in intelligence, preparedness, statesmanship, and historical contingency and unpredictability. Such lessons are relevant as America enters a period of great power competition with the People’s Republic of China, whose forces joined the war in October 1950 and are the reason that North Korea exists today.

As chairman of the House Select Committee on the Chinese Communist Party, Mike Gallagher has held a series of high-profile hearings on the threat that Communist China poses to American liberty, security, and prosperity. He is among the most important foreign-policy voices in the GOP and a rising leader in his party. His view of this contest for global supremacy ought to be taken seriously. Korea was the last war in which America fought China directly. The results were bitter. Recalling what happened, and why, is a necessary step toward deterring future conflict. You can see why Gallagher might be interested.

Gallagher and MacLean explained the thinking behind their course on Korea in a recent piece for Foreign Affairs. They noted that the Chinese Communist Party has revived interest in the war as an exercise in national glory and a preview of Communist hegemony. American amnesia, they further noted, has two sources: an ambivalence bordering on anxiety over the war’s outcome and a refusal to come to grips with the political and diplomatic mistakes that extended the killing. Their article earned a rebuke from China’s propaganda outlet Global Times, which likened Gallagher to MacArthur. Apparently this is a bad thing. (MacLean, for his part, went missing in the Global Times piece — much like China’s former foreign minister.)

“In its last war with China,” wrote Gallagher and MacLean, “Washington failed to deter its adversaries, failed to prepare its military, and prolonged the fighting, ultimately accepting outcomes in 1953 that would probably have been available in 1951 had it adequately projected its own resolve.”

Refusing to acknowledge and correct these errors is a sure way to repeat them. And repetition is unacceptable. China is politically, economically, technologically, and militarily stronger than it was seven decades ago. “The next time,” Gallagher and MacLean wrote, “the stakes will be even higher — and Washington must do better.”

The classes I attended were more about the historical record than future scenarios. Both Gallagher and MacLean served in the Marine Corps, and they drew on their military backgrounds while guiding the rest of us through the operations of the war at the strategic and tactical levels.

Not that the students needed help. They seemed to have memorized and analyzed the course materials. And they were eager to debate Secretary of State Dean Acheson’s January 1950 speech omitting Korea from America’s “defensive perimeter,” General Douglas MacArthur’s landing on the Incheon Peninsula, General Matthew Ridgway’s providential genius, and President Harry Truman’s relationship with top brass. I came away impressed by the quality of our future leaders. Their intellect was genuine, not artificial.

The same can be said for the professors. MacLean has taught at the U.S. Naval Academy, as well as for the Tikvah Fund, the Hudson Political Studies Program, and the Hertog Foundation, and his pedagogical talents were on display. And Gallagher was excellent. He managed the discussion, weaved in sources not mentioned in the syllabus, and drew inferences from, and made connections between, texts. He enjoyed reading aloud MacArthur’s exploits as well as tales of personal heroism at the unit level. At one point, he proudly announced that the lone vote against the Kellogg-Briand Pact of 1928 “outlawing war” came from Wisconsin Republican senator John J. Blaine. Gallagher had done his homework — and it’s not like he has a lot of spare time.

Perhaps the biggest star of the week was T.R. Fehrenbach, the late Texas journalist and historian whose 1963 book This Kind of War was required reading. Fehrenbach served in the Army during Korea, a fact never mentioned in 483 pages of gripping narrative. His history toggles between grand statesmanship and individual experience, and it leaves an indelible impact. You feel the chilling cold, the lack of supplies, the fear of the enemy, the physical and mental strain of combat. Fehrenbach’s clipped language, short paragraphs, and occasionally odd syntax bring you into the foreign country of the past. His book is a classic that should be taught in high schools.

Fehrenbach fixes his authorial eye on citizen soldiers. As I read his masterpiece, I thought of the Ukrainians fighting for their national existence, of the Taiwanese who might have to do the same, of the South Koreans keeping watch over their home, and of the more than a million American servicemen and women who defend the frontiers of freedom to keep our territory secure.

Among the lessons of the Korean war is that America is a force for good, American commitment produces a freer, safer, and more prosperous world, and the burdens of responsibility are real and enduring. I recall a passage of This Kind of War that we read aloud in class. Describing the battered U.S. soldiers who during the first months of the war fought a rearguard action from Seoul to the southeast corner of the peninsula, Fehrenbach wrote, “They were learning something they had not been told: that in this world are tigers.” And tigers must be caged.

Matthew Continetti is a senior fellow at the American Enterprise Institute and the founding editor of The Washington Free Beacon. For more from the Free Beacon, sign up free of charge for the Morning Beacon email.