Era guide · 1898–1901
Private Mailing Card era
The American postcard begins, formally, with the Act of Congress of May 19, 1898, which allowed private printers to produce cards mailable at the one-cent rate — provided they carried the words “Private Mailing Card.” That required phrase is the era's fingerprint: if your card says it, you're holding one of the oldest postcards in American circulation.
The entire back of these cards was reserved for the address. Any message had to fit on the front, squeezed into margins or written across the image — which is why golden-age and pioneer cards with handwriting on the picture side aren't damaged; they're used exactly as designed. In December 1901 the Post Office allowed the simpler imprint “Post Card,” and the Private Mailing Card wording faded out, closing the era.
Dating within the era: a postmark is the strongest evidence at this age. Cards printed before 1898 exist — souvenir cards and government postals go back further — but the “Private Mailing Card” imprint itself bounds your card to roughly 1898–1901.