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  • James Houser

July 20, 1592 - The Imjin War, the Samurai Invasion of Korea

Updated: Jun 12, 2021

July 20, 1592. The Japanese armies of Toyotomi Hideyoshi capture Pyongyang, completing a samurai blitzkrieg across the nearly helpless kingdom of Korea. While victory is in their sights, it is only Round One of the conflict known as the Imjin War. Soon the Koreans will start fighting back – and they will have help as the massive armies of China stream in from the north. It is the most epic war that most Westerners have never heard of.


Japan had waged an agonizing and dynamic struggle between its great samurai lords for generations, but by 1590 the empire was reunified for the first time in decades. All the great lords had been subdued or killed, all but one – and he was the strangest of all. His name was Toyotomi Hideyoshi.


Unlike many of his opponents, who were born into noble families of extended lineage, Hideyoshi was born a peasant of the lowest rank and never had anything given to him. In the turmoil that was Japan’s Age of War, he wound up as a foot soldier for the weak Oda clan – literally an infantry private. Somehow he got onto the staff of that clan’s young warlord Oda Nobunaga, who was fated to rise up and become the most powerful warlord in Japan. Much of his success was due to the diplomacy, genius and intuition of his talented young aide, who rapidly rose from courier to staff officer to general. Hideyoshi literally rose from nothing on his own merits to become Oda Nobunaga’s right-hand man.


In 1582, Oda was assassinated by one of his subordinates, and with his death it looked like his vast network of territories and alliances would fall apart. Instead, Hideyoshi took up a quest for vengeance on his master’s behalf and defeated and killed Oda’s murderer in battle. Then he took his dead mentor’s military machine and set it to work in a series of relentless and brilliant campaigns. By 1590, the defeat of the Hojo clan and the fall of Odawara Castle closed the book on the Age of War. For the first time since the Imperial City of Kyoto had been burned in the battle of clans and families, Japan was reunified once again.


Its new warlord was one of Japan’s unique historical figures. His appearance was bizarre, being described by Oda Nobunaga as that of a “little monkey” and by others as resembling a naked mole rat. He was brilliant, but absurd and subject to whims. Hideyoshi was an amazing planner, diplomat and general, but confused most Japanese lords with his almost whimsical manner and the “unseemly” affection he showed his family. At least one story has him softly singing to his infant son during war councils. Like many people who have gone from having nothing to being fabulously rich, Hideyoshi’s displays of wealth and power were ostentatious and tasteless.


Hideyoshi also had magnificent visions of his own destiny. By 1590, he had gotten it into his head that he was not only destined to rule Japan, but all of Asia. He was aware that his health was beginning to falter, and with the death of his son and brother in 1591 the succession was suddenly in dispute. With a burning desire to expand his already enormous legacy, and dreams of himself as warlord of all Asia, he decided to invade and conquer China. To do that, though, he would first have to conquer Korea.


Korea was a unified kingdom under the Joseon Dynasty in 1592, only a few miles off the coast of Japan’s southern island Kyushu. In sharp contrast to war-torn, battle-hardened Japan, Korea was a stable but insular country. Its only major threats were the latent Manchu tribesmen to the north and the East China Sea’s wokou pirates, each of which was held off with a small border guard. Korea’s army was underfunded and held little prestige; greater attention was paid to internal development, art, and administration. Korea did not grasp the danger it was in; it had kept an eye on developments in Japan, but never suspected that Hideyoshi would be foolish enough to invade them. After all, Big Brother was right around the corner.


Big Brother was Ming China, East Asia’s superpower. China and Korea had a tributary relationship: Korea managed its own affairs pretty much however it pleased, but simply paid a yearly tribute to the Heavenly Kingdom and received protection in exchange. Unfortunately for Korea, Ming China was even less clued into Japanese ambitions than Korea was. Most of China’s armies were fighting Mongolian tribes in the far north, or putting down rebellions in the south. There was no army ready in case the Japanese invaded.


Hideyoshi began planning and preparing for a massive invasion of Korea. Given the last, oh, 130 years of war, Japan was full to bursting with professional veteran soldiers and experienced commanders. Hideyoshi built an entire fortress at Nagoya on the western coast to serve as the mobilization center for the invading forces. He finally pieced together almost 225,000 men and 2,000 ships to prepare for the great expedition. In comparison, the Spanish could put together no more than 55,000 men and 130 ships for the invasion of England four years earlier (which I talked about yesterday). This demonstrates the vast power and potential of Japan at this stage in history.


The core of the Japanese army were the samurai, the military caste who dominated Japan. They served as commanders, officers and cavalry; they wore the giant lamellae armor and carried the katanas and yari so familiar to Western ideas of Japanese warriors. The main strength of Hideyoshi’s army were, deceptively, the peasants. Many of these peasants were armed with spears or bows, but a large number were trained and experienced in the use of the tanegashima – the musket. The peasant musketeer was the hidden strength of the Japanese army, trained to fight in the European style with rolling volleys that could shatter armies fighting in the old style.


The commanders of the invasion force were Konishi Yukinaga, a Catholic convert known to the Spanish and Portuguese as Dom Agostino, and Kato Kiyomasa, known as the “devil general,” whom the Koreans would later call the “young tiger.” Konishi would lead the first wave, and had been chosen for diplomatic rather than military reasons. Kato was not just a fierce general, but legendary for his personal fighting ability and his militant, violent Buddhist philosophy. Their religious differences would keep the two generals on bad terms throughout the campaign.


Konishi’s initial force of 7,000 men stormed ashore near Busan on May 23, 1592. The Korean navy detected the Japanese fleet, but the Korean fleet commanders at first ignored the possible threat. When the Japanese did arrive, most of the Korean admirals panicked, burning their vessels and fleeing into the hinterland. The powerful Korean fleet had large vessels armed with cannon, while the Japanese had almost no artillery on board their vessels; none of the Korean advantages counted, though, if the Korean admirals were too scared to fight.


Konishi demanded that the Koreans surrender their arms and allow his army to pass, saying that their target was China, but the Korean commander refused. Konishi quickly stormed the forts around Busan; his musketeers sniped the enemy commanders, causing resistance to collapse quickly. By May 25, Konishi and his army had conquered Busan and its surrounding cities, and were marching north with Seoul as their target.


The Japanese were merciless in their campaign. Konishi and Kato stormed multiple fortresses and cities, usually massacring the entire garrison. The capture of the city of Dongnae on May 25 resulted in the military garrison of 3,000 being butchered, as well as almost 20,000 civilians being put to the sword. Even the cats and dogs of Dongnae were hunted down and killed. Japanese ferocity was borne out of cultural superiority and racism. They had planned to use Korea as a route to invade China, who they regarded as the true opponent, and seemed almost insulted by Korean resistance. The Japanese were brutal to the Koreans in a way that presaged their behavior in the Second World War: they often massacred villages while taking Korean women as sex slaves. One of our most vivid accounts of some later battles comes from a Korean woman taken as a concubine who later wrote down her experiences.


Konishi’s army of 18,000 confronted 100,000 Korean troops at the Choryong pass blocking their way to Seoul. The Korean commander decided not to fight in the pass, but to engage the Japanese in open battle near Chungju. His cavalry charged over an open field and right into the teeth of Konishi’s musketmen, who had been placed to fire from two directions on the incoming attack. The Korean cavalry were slaughtered, and the Japanese muskets shredded attacks by archers whose arrows could not match their range. The disaster at Chungju set the tone for the Imjin War: engaging the Japanese in battle on their terms was near pointless.


Kato’s troops were soon following Konishi, with Kato furious that Konishi had not waited. He accused his rival of wanting all the glory for himself, and soon the two men were nearly at blows. Their mutual antipathy forced them to take two different invasion routes through Korea, which allowed them to cover more ground but would also keep them separated and unable to support each other if the situation changed. Nevertheless, the Japanese reached Seoul on June 10. From here on, the two proud samurai leaders would go their separate ways deeper into Korea.


Konishi Yukinaga advanced northward, sacking and burning the cities in his path. Kato Kiyomori advanced northeast, all the way to the border of Korea and China. On July 20, 1592, Konishi captured the city of Pyongyang, the final major city in Korean hands, and captured 100,000 tons of military supplies and grain. Konishi rested only briefly before he continued marching north. His destination was China. It looked for all intents and purposes like the Japanese conquest of Korea was a done deal.


But it wasn’t. Despite all the Japanese victories, they were on the precipice of disaster. And the reason was one man.


Yi Sun-Sin is, rightfully, the Korean national hero and is my personal candidate for the title of “greatest admiral in history.” The beginning of the Imjin War and the Japanese invasion, like I mentioned, saw the Korean admirals stunned and demoralized by the sudden attack. They burnt their ships and stores and led their crews inland in fear and shock. Soon all the Korean navy’s squadrons were gone or going – all but one.


Admiral Yi had not panicked or fled. Alone among Korean commanders, he had drilled and disciplined his small squadron to its highest potential. Of the 300 ships in the Korean Navy, 200 had been lost in the first days of the war, and the others were on the west coast, far beyond any hope of interfering. Yi only had 43 Korean ships left in his squadron to confront the 2,000 vessels of the mighty Japanese flotilla – but the Korean ships and crews were better, and this was Yi Sun-Sin.


Yi attacked, utterly surprising Japanese fleets with his tactics and speed. At Okpo on June 16, even as Konishi’s army marched into Seoul totally unconcerned with what was going on to their rear, Yi and his small fleet began their rampage by sinking 50 Japanese ships. At Sacheon on July 8, he spearheaded his attack with his own invention – the heavily-armored “turtle ship” that bristled with cannon and had an iron-plated roof, thus preceding the Merrimac by 250 years as the first step to an “ironclad.” The battles are too many to name; for the next five months, Yi Sun-Sin dominated the southern Korean coast, smashing Japanese fleets into matchsticks everywhere he appeared.


Yi’s combat record is almost too impressive to be believable, but it is confirmed by both Japanese and Korean records. To cap off his magnificent naval campaign, he sailed into Busan harbor with only 166 ships to confront the main Japanese navy of 470. As Toyotomi Hideyoshi himself watched, appalled, from the coast, Yi wrecked the Japanese fleet and destroyed 128 warships with only a few of his own damaged. In 15 separate engagements throughout 1592, Yi Sun-Sin never lost a single battle, and inflicted staggering losses on the Japanese navy. His knowledge of the terrain, brilliance in tactics, and sheer audacity stunned and overawed his opponents.


The Japanese had won a decisive victory on land. They had overrun Korea, captured its major cities, sent its King fleeing to China, and destroyed its armies. But Korea had won the war at sea, and this ended up being the war that mattered. As Konishi and Kato pushed deeper and deeper into mainland Asia, they began to realize the trouble they were in. Without the Japanese fleet to bring reinforcements and supplies from Japan, they would receive no more troops, ammunition, or even money to pay their men. Their amazing drive across Korea had seemed like a glorious victory, but the farther they went, the deeper they put their head into the trap.


It got worse for Hideyoshi and his armies. The Japanese had moved so fast that the lands behind them remained effectively unconquered, and soon the countryside was filled with Korean militias and guerrillas that choked off supply routes and destroyed isolated forces. The stupid Korean generals had all been killed; the smart ones, the ones who could learn from their mistakes and develop ways to fight the samurai war machine, were now leading the resistance. Admiral Yi’s fleet had ruined the Japanese Navy so badly that men had to be pulled from the land forces to man warships.


Finally, even as Konishi Yukinaga prepared to march north, he got word that a new army had showed up at his gates. They were a small force of 5,000 cavalry, a force he easily defeated – but the numbers were less important than their flag. They bore the banners of Ming China. The dragon had finally awoken, and was about to pour troops into Korea.


The Japanese were outnumbered, far from home, cut off from reinforcements and supplies, and were about to face down the giant of the East. Toyotomi Hideyoshi was about to learn that even the greatest ambitions have limits.


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