A Fortified District is a territory within which a system of defensive fortifications was constructed by the Japanese Army and in certain cases the Japanese Navy during World War II. A district was created in order to prevent invasion and provide a base for offensive operation. These fortified districts were built in the area of Manchukuo; Chosen in Korea; Karafuto; Southern Sakhalin and the Kurile Islands - a front of over 6,000 kilometers.