In late April or early May 1592, 豊臣秀吉 (Toyotomi Hideyoshi) stood at the highest tower of Nagoya Castle on the Kyushu coast and looked east across the Korea Strait. He was fifty-five years old, born in poverty, risen through sheer ferocity and cunning to become the undisputed ruler of Japan — and now he had run out of enemies at home. The staging fortress had taken over a year to build, funded by daimyo (feudal lords) across Japan who were too afraid to refuse. At its peak, the base held roughly 260,000 men including reserves — one of the largest concentrations of military force anywhere in the world in 1592.

The invasion order Hideyoshi issued set in motion more than 158,000 warriors organized into nine divisions, supported by a navy of 9,200 mariners. It was the largest overseas military expedition Japan had ever launched — a record that would not be broken for three and a half centuries. The objective was breathtaking in its ambition: conquer Joseon Korea, then use it as a road through which to march into Ming China and establish a Japanese empire with its seat of government in Ningbo.

At the head of the invasion's two lead columns stood men who symbolized the internal fault lines of Hideyoshi's realm. 小西行長 (Konishi Yukinaga), commanding the First Division of roughly 18,700 men, was a Catholic Christian convert known to Portuguese traders as Dom Agostinho. He had converted in 1583 and brought a diplomat's temperament to a soldier's war. 加藤清正 (Katō Kiyomasa), commanding the Second Division of more than 20,000 men, was a fanatical Nichiren Buddhist who loathed Konishi on every level — personally, politically, religiously. The two commanders barely communicated during the campaign, advancing on separate axes to avoid the discomfort of cooperation.

The opening weeks were staggering in their speed. Japanese troops landed at Busan on approximately May 23, 1592, and Seoul fell in roughly eighteen days. 加藤清正 (Katō Kiyomasa) pushed all the way to the Yalu River on the Manchurian border. 小西行長 (Konishi Yukinaga) captured Pyongyang. Back at Nagoya Castle, Hideyoshi began planning the logistics of governing China. He wrote to the Ming Emperor in terms suggesting the conquest was already complete — a letter staggering in its presumption.

Then Ming China entered the war. The imperial army that crossed into Korea reversed the Japanese advance, and what had begun as a lightning campaign became something else entirely: a grinding war of attrition fought across occupied Korean territory, sustained by supply lines stretching back across the Korea Strait, against a population that did not want to be liberated.

Hideyoshi died on September 18, 1598, still refusing to acknowledge failure. His generals secretly negotiated a withdrawal. The 朝鮮出兵 (Chōsen Shuppei — dispatch of troops to Korea) had killed or displaced hundreds of thousands of Koreans. Korean artisans, potters, and scholars were taken back to Japan as captives, inadvertently transmitting elements of Korean culture that influenced Japanese ceramics and Neo-Confucian thought for generations. The scars on the peninsula ran deeper and lasted longer.

In Japan, the war consumed the treasury and fractured the alliances that might have secured the Toyotomi succession. 小西行長 (Konishi Yukinaga) and 加藤清正 (Katō Kiyomasa) — the Catholic and the Buddhist who had refused to cooperate in Korea — chose opposite sides at the Battle of Sekigahara in 1600. The Korean disaster did not cause Tokugawa Ieyasu's victory, but it cleared the board for it. The man who had warmed Nobunaga's sandals had, in his final gamble, handed Japan to someone else.