Veteran's Day was first known as Armistice Day, celebrating the end of fighting in World War I. It was first proclaimed in 1919, but not made into a Federal holiday until 1938. Thanks to the efforts of citizens of Emporia, Kansas it became a celebration of all veterans in 1954.
The three generals portrayed in this stamp were leading Union commanders during the Civil War. Ulysses S. Grant commanded troops in the Western Theater, eventually becoming commander of all Union forces. After the war he was elected President of the United States in 1868. Sheridan and Sherman continued to serve in the Army, fighting in the Indian Wars of the later 19th Century.