Stephen Turnbull 
Japanese Castles in Korea 1592 98 [PDF ebook] 

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 fortifications were never developed or modernized after the Japanese departure. The details of late 16th-century castle construction are therefore better preserved than at many other sites. Written by Stephen Turnbull, an expert in the subject, this book examines the castles built by the Japanese in Korea, as well as the use made of existing Korean fortifications, particularly city walls. This resulted in curious hybrid fortifications that dominated the landscape until the Japanese were pushed out of the peninsula by a furious onslaught from huge Chinese armies.