In 1942, President Franklin D. Roosevelt, an avid stamp collector, asked the U.S. Postmaster General to issue a series of stamps to honor the European nations that had been overrun or occupied by the Axis powers during World War II. First day covers are envelopes or postcards with a stamp canceled on the first day the stamp is available for purchase and use. Often the postmark is a special pictorial cancellation indicating the city and date of issue. First day covers often include a cachet or illustration on the envelope that explains or compliments the stamp.https://digitalcommons.fairfield.edu/firstdaycover/1005/thumbnail.jp