U.S.A.: We Appreciate Our Servicemen

"We Appreciate Our Servicemen" U.S. patriotic stamp issued in 1966. I could not find why the card also has 'Fort Sumter National Monument in South Carolina' text on the front. But the card was sent to me from there, the place where the American Civil War began in 1861. And I've got special postmarks!

Private swap. Thanks, Erin!