The Imjin War (1592-1598) was not simply a conflict between Korea and Japan. It was a seven-year international war that shook the entire power structure of East Asia. To understand Toyotomi Hideyoshi's motivations for invasion, we must look at Japan's political situation at the time. Having unified Japan after 100 years of civil war in the Sengoku period, Hideyoshi needed to redirect the energy of dissatisfied daimyos and surplus military forces outward. His vision — 'conquer Joseon, seize Ming China, advance to India' — sounds like megalomania, but Japan's military power at the time was genuinely world-class. Japanese forces possessed the world's largest arquebus army equipped with teppo (firearms), and Joseon's army was completely unprepared to face them. At sea, however, the situation was entirely different. Yi Sun-sin's navy, led by the Turtle Ship and Panokseon warships, severed Japan's supply lines, and this became the decisive factor turning the tide of war. Japan's land forces, victorious in battle after battle, suffered repeated naval defeats and fell into strategic stalemate. The prolonged war exhausted not only Joseon but Japan and Ming China alike. Ming China, having poured enormous military power and finances into the war, experienced rapid national decline — directly contributing to the Manchu founding of the Qing Dynasty and the fall of Ming. Joseon too suffered unprecedented devastation, losing 30-40% of its population and seeing two-thirds of its farmland laid waste. Yet paradoxically, the war catalyzed fundamental reform of Joseon society. The righteous army movement shook the established social order, and the emergence of war heroes forced a revaluation of warrior culture within the Confucian literati-centered tradition. The Imjin War was a decisive inflection point in East Asian history.