text: Direct diffusion occurs when two cultures are very close to each other, resulting in intermarriage, trade, and even warfare. An example of direct diffusion is between the United States and Canada, where the people living on the border of these two countries engage in hockey, which started in Canada, and baseball, which is popular in American culture.
  Forced diffusion occurs when one culture subjugates (conquers or enslaves) another culture and forces its own customs on the conquered people. An example would be the forced Christianization of the indigenous peoples of the Americas by the Spanish, French, English, and Portuguese, or the forced Islamization of West African peoples by the Fula or of the Nuristanis by the Afghans.
  Indirect diffusion happens when traits are passed from one culture through a middleman to another culture, without the first and final cultures being in direct contact. An example could be the presence of Mexican food in Canada since a large territory (the United States) lies between.
  Direct diffusion was common in ancient times when small groups of humans lived in adjoining settlements. Indirect diffusion is common in today's world because of the mass media and the invention of the Internet. Also of interest is the work of American historian and critic Daniel J. Boorstin in his book The Discoverers, in which he provides a historical perspective on the role of explorers in the diffusion of innovations between civilizations.
  Theories
  The many models that have been proposed for inter-cultural diffusion are: