The thirteenth and last stamp in the Overrun Countries series, issued on November 2, 1944, features the flag of Korea, the only non-European country to be so honored. Korea had been occupied by the Japanese since 1910. During this period, Korean culture had been suppressed and the country had been modernized to Japanese standards. During World War II, the occupation became harsher, with many Koreans subjected to forced labor there and in Japan. Japan diverted most Korean resources to its war effort.