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.
The Japanese forces had built 17 "fortified districts" and over 4,500 permanent emplacements along the USSR border.
In similar form it organized other fortified districts inside mainland Japan (coastal and inner mountainous areas) and overseas provinces (Taiwan, Ryukyu, South Seas Mandate, etc.)