 In accordance with Article VI of the Constitution, on that date this treaty became incorporated as part of "the supreme Law of the Land".Since the 1940s, the Jehovah's Witnesses have often invoked the First Amendment's freedom of religion clauses to protect their ability to engage in the proselytizing (or preaching) that is central to their faith.This series of litigation has helped to define civil liberties case law in the United States and Canada.