The twelfth European country to be recognized by the Overrun Countries Series was Denmark, whose flag is featured on a stamp issued December 7, 1943. Germany invaded Denmark on April 9, 1940. Having little military strength, the Danes did not resist. Denmark was treated relatively well during the occupation, largely because Germany considered its agricultural output crucial to its war effort. As the war dragged on, though, resistance increased, and the occupation became harsher.