Key point: Beijing's surprise invasion should not have been as much of a surprise, but America was caught off guard and suffered as a result.

On June 25, 1950, the North Korean People’s Army (NKPA) under Marshal Kim Il-sung launched a no-notice invasion of South Korea. Many are familiar with the failings of “Task Force Smith” in the first week of the war and MacArthur’s brilliant landings at Inchon that September. Few, however, realize the decisive moment of the war came three months after Inchon, amidst the most brutal cold wave imaginable, at a place called the Chosin Reservoir. American arrogance and bigotry forfeited what could have been a spectacular strategic victory.

Our current nuclear standoff with Kim Jong-un is, in large measure, the bitter fruit of that failure.

For the United States, the war started off disastrously. After their surprise attack, Kim’s forces blew past the badly outgunned and outmatched South Korean military forces north of Seoul, and continued the march south. Near the city of Osan, about twenty-five miles south of Seoul, America’s first combat unit, 120 men of Task Force Smith, set up a defensive position to block the NKPA’s drive south.

American leaders expected that when the North Koreans saw U.S. troops, they would stop their advance or even run away. But in a classic example of unpreparedness resulting from years of neglected training and equipping with modern weapons, the T-34 tanks of the North’s lead elements virtually destroyed Task Force Smith and continued the attack. The United States and allied nations rushed to get more combat power into South Korea before the North could capture the southern port of Pusan.

The North’s drive started to stall by September, and on September 21, Gen. Douglas MacArthur executed a surprise landing on the coast west of Seoul at Inchon, sending the NKPA into a full retreat. The allied forces then began a devastating counterattack to the north that within two months had conquered almost all of North Korea.

On November 23—Thanksgiving Day—the Americans were jubilant, some enjoying actual turkey dinners within view of the Yalu River, which marked the border with China. MacArthur told troops the war was in hand and would probably be over by Christmas.

Unbeknownst to most of those happy troops, however, was that MacArthur and many of his senior intelligence officers had received numerous reports of massive Chinese troops buildups north of the Yalu. They discounted them all, however, believing the Chinese to be backward and vastly inferior, and thus rejected the notion they would attack.

Besides, MacArthur had planned what he expected would be the final thrust to the Yalu and the end of the war. He didn’t want his timetables disturbed. His dismissal of the warnings, and the arrogant assumption that his attack would succeed anyway, condemned thousands of Americans to their deaths and forfeited what otherwise might have been the complete conquest of the Korean Peninsula.

The northeastern prong of MacArthur’s final push included fifteen thousand troops made up of the First Marine Division and the Army’s Seventh Infantry Division, positioned for the attack on either side of a large lake known as the Chosin Reservoir. After the sun went down on November 25, however, thousands of Chinese troops seemingly came out of nowhere and swarmed into both the Marine and Army units, causing significant casualties. As the sun came up, however, the Chinese didn’t press the attack, and withdrew.

MacArthur was concerned by the attack, but considered it a minor episode, likely a weak attempt to spoil the American offensive. He ordered the Marines and soldiers to remain on schedule and attack on November 27 as planned. Aside from the difficulty of the mountainous terrain, the lake that separated the U.S. force and the possibility of many Chinese soldiers, the weather turned against the Americans: temperatures fell on September 27 to zero degrees. Later, it would plunge to nearly 30 degrees below zero.

But before the U.S. attack got fully underway, U.S. leaders were again surprised—shocked, this time—when they were suddenly attacked from multiple directions by six Chinese infantry divisions, comprising more than sixty thousand troops. MacArthur had correctly assessed that a typical Chinese soldier was vastly inferior to his U.S. counterpart in terms of training, experience and equipment. What he failed to consider, however, was their sheer numbers, utter fearlessness and total dedication to the mission regardless of cost.

When the Chinese unleashed the full fury of their attack on November 29, the U.S. troops were caught off guard and staggered under the onslaught. The Army units on the east side of the lake caught the worst of it, however, because there were fewer of them. The Marines were unable to provide any assistance because of the lake that separated the two forces.

The nighttime attack caused great confusion for the Americans, and no small number of casualties. But when the sun came up the next morning, the Chinese had again withdrawn. MacArthur had disdain for the Chinese, and regarded them as a “peasant army” not worth worrying about; he ordered the previously scheduled attack to the Yalu to continue.

Mao Zedong, however, had studied MacArthur and detected a weakness: his hubris. He withdrew after the attack on November 29, gambling that the American would consider China’s forces inferior and immediately pursue. MacArthur took the bait and ordered the northward attack to immediately resume.

Because the Marines and soldiers were limited to narrow mountain roads and could not assist each other because of the lake, the Chinese took full advantage and began further dividing the U.S. troops, sending overwhelming numbers of soldiers against small, isolated contingents of Americans. On December 1, as casualties began to mount, the reality of the strength of the Chinese attack struck home, and U.S. forces began a fighting withdrawal to the Sea of Japan, still some eighty miles away.

By the time the Army units east of Chosin began their withdrawal, they had already incurred more than four hundred wounded. The troops gathered every truck vehicle that was still operational, loaded everyone aboard, wounded or not, and began the withdrawal; though a gut-wrenching decision, they was no room in the trucks and had to leave the dead where they fell. They began the march with approximately 2,500 soldiers. The convoy, however, would never make it to secure American lines.

For practically every yard of the trip, the Chinese were attacking the road-bound American retreat from the mountains above. One by one, the vehicles were shot out from under the soldiers. At first they transferred the survivors to other vehicles. As the losses piled up, however, there was no longer any room on the serviceable trucks. Eventually every single truck was knocked out.

The men were told to infiltrate through enemy lines as best they could to try and link up with the Marines south of the Chosin. Snowstorms picked up their intensity, and temperatures plunged to 30 below zero just as the U.S. troops lost all means of conveyance. Almost as many Americans suffered debilitating frostbite as enemy bullets.

The Army troops were forced to do the unthinkable: they had to leave each and every wounded man behind to have any chance of surviving the attacking Chinese. Of the 2,500 who began the withdrawal on December 1, fewer than 350 made it back to U.S. lines in fighting shape.

Mao believed that if he could push one of America’s most famous generals out of North Korea, he could cause great fear and doubt in Washington, which he could use to strategic advantage. Though his forces suffered a staggering fifty thousand casualties of their own, Mao was ultimately proven right: the Americans would never again threaten to overrun North Korea. An armistice was eventually signed on July 27, 1953, setting the border between North and South Korea at its current location.

Had MacArthur and other U.S. leaders heeded the intelligence warnings of massing Chinese troops in early November 1950, they could have conducted a consolidating move to the south—without any interference from enemy contact—and set up a defensive position in better terrain that offered routes to provide mutual support between units. Had the Chinese troops been required to attack the United States in defensible positions where reinforcements could be brought to bear, it is likely Mao’s troops would not have been able to force the United States into retreat.

In that case, the battle would have been fought on terms advantageous to the United States, in positions that U.S. forces could have held, and once Chinese troop strength had been spent, then MacArthur could have pushed to the Yalu and ended the war in complete tactical and strategic victory, sending the Chinese back across their border in defeat.

Instead, the U.S. retreat resulted in another two years of indecisive war, the deaths of thousands more Americans and eventually the permanent, tense division of Korea. That division has necessitated the expenditure of hundreds of billions and more than six decades of military occupation to maintain security.