The siege of Otsu Castle was part of the Sekigahara campaign, during which the so-called Eastern Coalition, led by Tokugawa Ieyasu, fought against the Western Coalition, led by Ishida Mitsunari. Otsu Castle was built in 1586 by order of Toyotomi Hideyoshi near the capital Kyoto, on the site of the dismantled Sakamoto Castle. It belonged to the type of “water castles” — mizujō — as one side of it faced Japan's largest lake, Lake Biwa, and it was surrounded by a system of moats filled with lake water, which made the fortress resemble an island.
The siege of Shiroishi Castle was part of the Sekigahara campaign and took place several months before the decisive battle of Sekigahara. The daimyo of Aizu Province, Uesugi Kagekatsu, posed a serious threat to Tokugawa Ieyasu's plans to defeat the Western Coalition, and Ieyasu decided to curb his actions with the help of his northern vassals. To this end, he ordered Date Masamune to invade the province of Aizu and capture Shiroishi Castle.
During the two Korean campaigns of the 16th century, the Japanese repeatedly had to capture enemy fortresses and defend occupied or constructed fortifications from the combined Korean and Chinese forces. Among all the operations of that time, the second siege of Jinju Castle is considered the most interesting from the point of view of siege warfare.
The siege of Takamatsu Castle in Bitchu Province is considered the first mizuzeme, or “water siege,” in Japanese history. Until then, such an original tactic had never been used.
The history of the castle prior to the conflict between the Tokugawa and Takeda clans is rather unclear. According to one version, the castle was built in 1416, when Imagawa Sadayoshi (1325–1420) was governor of Suruga Province and half of Totomi Province. Allegedly, it was he who ordered Imagawa Norimasa (1364–1433) to build this fortification. However, no reliable evidence has been found to support this. Another version is considered more plausible, according to which the castle was built during the conquest of Totomi Province at the end of the 15th century by Imagawa Ujitsuna (1473–1526) and his general Ise Shinkuro (Hojo Soon). In this case, another of Ujitsuna's generals, Kusima Masashige (1492–1521), is considered responsible for the construction.
In 1556, the Shimazu clan launched a campaign aimed at systematically conquering the island of Kyushu. In the same year, the province of Osumi was annexed and a war began with the Ito clan for control of the province of Hyuga. In 1577, Ito Yoshisuke was defeated and fled north, where he sought help from Otomo Sorin, the Christian daimyo of Bungo Province.
