The Japanese invasion and occupation of Korea, which lasted from 1592 to 1598, was the only occasion in Japanese history when samurai aggression was turned against a foreign country. During the occupation of Korea the Japanese built 25 wajo or castles. Unlike the castles built in Japan, these castles were never developed or modernized after the Japanese departure meaning that the details of late 16th century castle construction are better preserved than at many other sites.

Written by Stephen Turnbull, an expert on the subject, this book examines the castles built by the Japanese in Korea, as well as the use the samurai made of existing Korean fortifications, particularly city walls. This resulted in curious hybrid fortifications which dominated the landscape until the Japanese were pushed out of the peninsula by a furious onslaught from the huge Chinese armies.