This article describes how draft or heavy horses were transformed into purebreds (by modern definition “breeds” rather than “types/classes”) in response to the demands of an export trade particularly to the United States. The history of Clydesdale and Percheron breeding in relation to the international market between Canada, Britain, and France with the United States between 1870 and 1910 illustrates how draft horse breeding changed because of trade patterns, and in doing so elucidates the infiltration of purebred breeding to the horse world.