When the North Koreans invaded on June 25, 1950, they reached the outskirts of the South Korean capital of Seoul the next day and overran it soon thereafter. From that point to the retreat of the American and South Korean forces south to the port of Pusan was only another three months.
The Nortk Korean invasion force included 10 infantry divisions, one armor division and an North Korean Air Force division. The size of the force was 100,000 to 200,000 men and roughly 275 Soviet-built T-34/85 tanks, 200 cannons (artillery) and about 250 front-line combat aircraft. In contrast, South Korea had about 100,000 men, no artillery, no tanks and no front-line combat aircraft. Both sides had minor vessels in their respective navies.
The North Korean forces were manned by many veterans of the Chinese Civil War that had just ended in 1948. Except a few hundred lightly armed men, the nearest American forces were in Japan, enjoying the good and easy life as the post-World War II occupation force in that ancient country.
By the time the fighting was around the Pusan Perimeter, the North Korean force was down to 90,000. But it had in no uncertain terms boxed the ROK and US forces tightly into the Pusan Perimeter, a rectangular foothold which about sixty miles tall. At the bottom right corner was the second largest city in South Korea: Pusan, after which the perimeter was named. It was not only the most important city held by the Allies, it was the lifeline to all of the combatants, residents and waves of refugees that had fallen in retreat.
At their back was the Korea Straight of the Sea of Japan which was bisected by Tsushima, a pair of islands made tremendously famous by the great Russo-Japanese naval battle which had taken place near there 45 years earlier in 1905. The Japanese won, sinking seven battleships and sinking or damaging 27 other ships in exchange for the minimal loss of three torpedo boats. The battle marked the first time in modern history that an Asian nation trounced a European one in battle. At the moment, it looked like another Asian nation was about to defeat another “European” one.
The feeling of being hemmed was greatly exacerbated by the ring of mountains surrounding Pusan. Indeed, the city’s name means “Teapot Hill.” With their backs to the ocean, there was nowhere else to go to, with the possible exception of a Dunkirk-like retreat by sea. But at that point, persuading anyone to execute a full-scale evacuation would have been nearly impossible and the loss of face for losing the Pusan area would have been tremendous. It also would have meant losing the war.
The situation was desperate. But everything changed in an instant at Inchon, a port city 20 miles southwest of Seoul. Inchon was General Douglas MacArthur's brilliant September 15, 1950 counterstroke and surprise invasion from the sea 200 miles behind North Korea's furthest penetration.
Interestingly, the Inchon landing was to be the last major amphibious assault in military history, at least to this day 60 years later. The invasion was brilliantly executed and the credit goes completely to General MacArthur who fought against the Truman Administration and others in the military to get his way. In spite of tides that went up and down an astounding 33 feet, MacArthur argued that not only could the invasion be pulled off successfully, but that it was the only way to save the troops penned up in the Pusan Perimeter and to save the war.
The invasion was carried out perfectly. There were few North Korean troops guarding Inchon and Seoul, and the ones who were there had not been tested in combat. The invasion not only cut across North Korea’s flank and logistical train, but it also served as a spring board to a rapid inland drive back to Seoul, just 20 miles away. And the American forces did just that. So the South Korean capital of Seoul was liberated on September 29, 1950 just three months after it first fell.
Psychologically unnerved and overextended in any case, the North Korean units had little choice but to dissolve, individual soldiers abandoning their equipment and weaponry and walking back to North Korea any way they could. Astoundingly, only half of them returned to North Korea alive. At that point, the US/ROK forces advanced north to the NK capital of Pyongyang, 120 air miles north of Seoul.
Pyongyang fell extremely rapidly, just within a month of the liberation of Seoul, on October 20, 1950. Such hyper-rapid capture and liberation of national capitals remains unprecedented in modern, and possibly all, warfare.
American and South Korean forces raced through North Korea toward the border of North Korea and China, hoping to not only knock North Korea completely out of the war, but to reunite it with South Korea and, by extension, bring it into the American sphere of influence.
The border was attained only in one place: to the north east at Hysanjin on November 24, 1950. The war was almost five months old.
Staring across the border was China: specifically the People's Liberation Army (PLA). The subet of the PLA amassed on the border it called the People's Volunteer Army (PVA). China had been ripped apart by the recent Chinese Civil War which had been fought by millions of men over about 25 years and which had left more than three million dead combatants in its wake. And that war was fought during World War II, which meant that the Chinese fought two major wars simultaneously. The Chinese were poor and as a nation they must have seemed tremendously weak to anyone naïve enough to forget 5,000 years of history. General Douglas MacArthur, the genius behind Inchon and self-styled Asia expert, was just that naïve man.
MacArthur, President Truman and other members of the Truman cabinet tragically miscalculated China's independence and resolve. The thinking China was controlled puppet of the Soviet Union and would not act without direct orders from Stalin. Stalin seemed unwilling to risk World War III over Korea, and thus would not order China to intercede in North Korea to defend it. But China was operating on its own, and felt extremely threatened by the American success in overrunning North Korea as much and as rapidly as it had so far.
The Chinese PVA forces smashed through US/ROK lines in places and forced a general retreat elsewhere. So once again the front changed directions, this time from north going back south in the general direction of the 38th parallel. Pyongyang was back in PRC/NKPA hands by December 5, 1950, only 10 days after the Chinese onslaught.