The United States Postal Service began issuing pre-stamped postal cards in 1873. Initially, the United States government prohibited private companies from calling their cards postcards, so they were known as “souvenir cards” instead. This monopoly was abolished on May 19, 1898, when Congress passed the Private Mailing Card Act which allowed private publishers and printers to produce postcards.
The first postcards in the United States in the modern sense of the term were created in 1893 to advertise the World's Colombian Exposition in Chicago. Soon after the United States Postal Service, allowed printers to publish a 1-cent postcard (the "Penny Postcard"). A correspondent's writing was allowed only on the front side of these cards (sometimes on a picture), with the address on the back. These are referred to as undivided back cards..
In 1907, the writing of a message was allowed on the back or address side of the postcard and allowed the introduction of the "divided back postcard." The left section of the card was used for the message and the right side for the address. This began what some collectors refer to as the Golden Age of American postcards, which is noted for its many elaborate and beautifully illustrated cards, many printed in Germany. The era ended about 1915, when the onset of World War I blocked the import of these fine German-printed cards.
Based on this history, and subsequent eras of changing designs of postcards, US postcard collectors generally break out the eras and designs of postcards as follows:
- Pioneer Era Souvenir Cards (1867-1898)
- Private Mailing Card Era (1898-1901)
- Real Photo (a design type of cards using real photographs; began about 1901 and continues to today)
- Undivided Back (begins 1901when private "postcards" officially allowed to 1907)
- Divided Back (1907-1915)
- White Border (1915 to 1930; a white border introduced on the front as a design element)
- Linen (1930 to 1945; cards printed on textured cardstock with the appearance of linen)
- Chrome (1945 to 1970; color picture postcards, measuring 3.5 x 5.5 inches, and continuing to today
- Continental 1970 to present, same as chromes, but 4 x 6 inches