what two countries popularized halloween costumes

Scotland and Ireland are the two countries that popularized Halloween costumes for trick-or-treating. The wearing of costumes during Halloween may have originated in a Celtic festival held on October 31st to mark the beginning of winter, which was called Samhain in Ireland, Scotland, and the Isle of Man, and Calan Gaeaf in Wales, Cornwall, and Brittany. Halloween costumes were popularized in the United States by adults in the late 1800s, but by the early 1900s, they were worn mainly by children. In the 1930s, companies began mass-producing Halloween costumes for sale in stores as trick-or-treating became popular in North America.