Chosokabe unified Shikoku in 20 years — Hideyoshi took three-quarters back in two months

Chosokabe Motochika started as lord of a single castle in Tosa province and spent roughly two decades fighting his way across Shikoku. He beat the Motoyama clan in 1562, destroyed the Ichijo family in 1575, took Iyo province by 1580, and finished off Awa and Sanuki by 1583. That year he became the first person in the island's history to control all four of its provinces outright.

He had almost no time to run it. Toyotomi Hideyoshi, who had just consolidated power over most of Japan, sent an invasion force of about 113,000 men against Motochika's roughly 40,000 in 1585 — nearly three attackers for every defender. The campaign was fast: after a 26-day siege of Ichinomiya Castle, Motochika surrendered within about two months of the invasion beginning.

Hideyoshi let him keep Tosa, the province he had started from twenty years earlier, and handed Awa, Sanuki and Iyo to his own generals. The two decades of campaigns that had built Motochika a four-province domain ended with him back to a one-province vassal, now answering to the man who had taken the rest.

The unification itself was not the error — someone had to eventually run into Hideyoshi's much larger, centrally organised army. The error was treating total control of the island as a finished goal rather than a new, larger exposure. Motochika had spent his resources and manpower reaching a scale that immediately drew the attention of a power he could not match, with no plan for what came after arrival.