Karatsu, Saga
Due to its proximity to mainland Asia, Karatsu has long been known as a stopover to Korea and China.Under ritsuryō, the current city area was part of the Hizen Province. In 1591, on the coast of the northern part of the city (formerly the town of Chinzei), Nagoya Castle was constructed. The following year, it became the location from which the Imjin War was launched by Toyotomi Hideyoshi. In the middle of 1593, Terasawa Hirotaka created the Karatsu domain and began governing it. In 1602, replacing Nagoya Castle, Karatsu Castle was constructed in what is now the heart of Karatsu. The tower of Karatsu Castle was built in 1966 .
Japanese invasions of Korea (1592–1598)
Hideyoshi planned for a possible war with Korea long before completing the unification of Japan, and made preparations on many fronts. As early 1578, Hideyoshi, then fighting under Oda Nobunaga against Mōri Terumoto for control of the Chūgoku region, informed Terumoto of Nobunaga's plan to conquer China. In 1585, Hideyoshi had told the Portuguese Jesuit Father Gaspar Coelho of his wish to conquer all of East Asia, and asked he sent a message to his master, King Philip II of Spain who as Philip I was also the King of Portugal, asking he make his navy available to help him, a request that was refused. The defeat of the Odawara-based Hōjō clan in 1590 finally brought about the second unification of Japan, and Hideyoshi began preparing for the next war. Beginning in March 1591, the Kyūshū "daimyōs" and their labor forces constructed Nagoya Castle in Nagoya, Saga (modern-day Karatsu, Saga, not to be confused with present day Nagoya city in Aichi Prefecture) as the center for the mobilization of the invasion forces. In 1592 Hideyoshi sent a letter to the Philippines demanding tribute from the Spanish governor general and stating that Japan had already received tribute from Korea (which was a misunderstanding) and the Ryukyus.