The concept of a Halloween card originated in the 1890s United States, experiencing a peak of popularity there in the early 1900s. Until the advent of the common home telephone, Halloween cards occupied a role similar to Christmas cards and birthday cards.

From about 1900 to 1915, the United States experienced a Halloween "postcard craze" that continued the commercialization of the holiday that began in the 1800s. The popularity of Halloween cards rivaled that of Christmas cards until about 1930, by which time telephones were common household items and began supplanting the use of greeting cards.

Of the over 3,000 cards produced in the United States during this period, many depicted themes common to the modern tradition, including witches, pumpkins, and goblins. Other Halloween postcard themes included fortune-tellingand romance or courtship. Designs also reflected the racism in the United States of the era:the most common theme being black children, appearing on 42% of cards depicting an ethnic or racial difference from the white majority.

Info from Wikipedia