Blackstone's Commentaries stated that the common law imposed a duty on parents to provide for the maintenance, protection, and education of their children, and of these, the duty to provide an education was "of far the greatest importance." Early on American courts cited Blackstone for the proposition of the common law duty of parents educate their children. As the nineteenth century progressed, public and private schools were formed in most American states, and a number of states enacted compulsory education laws. American states also sometimes also enacted laws that interfered with the freedom of parents to direct the education of their children. In 1919, in the wake of the anti-German hysteria of World War I, Nebraska passed a law that prohibited the teaching of German in the Lutheran sectarian schools. In 1922, Oregon passed a law prohibiting parents from enrolling their children in private and sectarian schools. The Supreme Court held that both of these laws were unconstitutional under the Fourteenth Amendment's due process clause, because they interfered with the liberty of parents to control the education of their children. In the United States, Blackstone's common law duty of parents to provide an education for their children had evolved into a constitutional right of parents to control the education of their children.