In the first month of Bunroku 1 (1592), Toyotomi Hideyoshi issued the formal mobilization order for the most ambitious military campaign in Japanese history: the invasion of Korea, and through it, the conquest of Ming China. The man who had risen from barefoot peasant to supreme ruler of Japan now intended to conquer the known world.

The ambition wasn't new. As early as 1585, Hideyoshi had told the Portuguese Jesuit Father Gaspar Coelho of his wish to conquer all of East Asia. He even asked King Philip II of Spain — who was also King of Portugal — to lend his navy for the effort. Philip declined, preferring not to provoke China. Hideyoshi was undeterred. He had unified Japan; the continent was next.

The scale of the mobilization was staggering. Beginning in March 1591, daimyō across Kyushu and their labor forces constructed Nagoya Castle in modern-day Karatsu, Saga Prefecture (not the more famous Nagoya in Aichi) as the staging ground. Roughly 335,000 men were mobilized nationwide. Of those, about 158,000 were organized into nine divisions for the crossing, with another 100,000 stationed in reserve across northern Kyushu and the rest of Japan. Some 700 transport ships were gathered from Kyushu, Shikoku, and the Chūgoku region. It was the largest overseas military expedition the world had seen up to that point.

Hideyoshi himself would not cross the water. He commanded from Nagoya, sending three of his most powerful generals to lead: Konishi Yukinaga, Katō Kiyomasa, and Kuroda Nagamasa. A quarter of the invasion force carried tanegashima — matchlock firearms — fired in devastating volley systems perfected during the decades of civil war.

The pretext was that Korea had refused to grant passage for a Japanese army marching to China. The real motivation was murkier. Hideyoshi may have genuinely believed he could topple the Ming dynasty. He may have needed a foreign war to keep hundreds of thousands of battle-hardened samurai occupied now that Japan was unified. Some historians point to megalomania — the peasant who had conquered everything in reach simply could not stop conquering. In one letter, he even addressed the Spanish authorities in the Philippines demanding they recognize Japanese supremacy.

The initial invasion was devastating. The first wave landed at Busan on May 23, 1592, and the port fell within hours. Japanese forces tore through the peninsula in weeks. Seoul fell by June 11. The Korean king fled north. Pyongyang was taken shortly after.

But then everything went wrong. Korean admiral Yi Sun-sin — commanding a fleet that included the iron-roofed geobukseon (turtle ships) — shattered Japanese supply lines along the western and southern coasts. Without secure shipping lanes through the Yellow Sea, the army couldn't be resupplied for a push into China. Meanwhile, bands of Korean guerrilla fighters known as uibyeong (義兵, "righteous armies") — including Buddhist monks — harassed Japanese positions across the countryside. And in January 1593, a Ming Chinese army of roughly 43,000 under General Li Rusong crossed into Korea and retook Pyongyang.

The war ground into a brutal stalemate. Peace negotiations dragged on for years, collapsed when Hideyoshi was insulted by the condescending tone of a Ming decree, and a second invasion was launched in 1597. It was smaller, more defensive in posture, and ultimately futile.

Hideyoshi died on September 18, 1598. The armies came home. As many as 50,000 to 60,000 Korean civilians were taken back to Japan as prisoners — many of them potters, whose craft would give rise to some of Japan's most celebrated ceramic traditions, including Satsuma, Arita, and Hagi ware.

The largest conflict of the sixteenth century — involving over 500,000 combatants from three nations — left Korea devastated, China weakened (and vulnerable to the Manchu conquest that came fifty years later), and Japan with nothing to show for it but teacups.