John C. Calhoun continued almost to the day of his death to modify his interpretation of the Constitution in the interest of his section. As a young man he avowed protectionist principles. Becoming convinced that slave labor was not suited to manufacture, he urged South Carolina to declare the protective tariff laws null and void within her limits. When his section seemed endangered by the distribution of anti-slavery literature through the mail, he extemporized a theory that each State had a right to pass statutes to protect itself in such an emergency, in which case it became the duty of the general Government and of all other States to respect such laws. When it finally appeared that the territory acquired from Mexico was likely to remain free, the same statesman made further discoveries. He found that Congress had no right to exclude slavery from any Territory belonging to the United States; that the owners of slaves had equal rights with the owners of other property; that neither Congress nor a territorial authority had any power to exclude slaves from a Territory. This doctrine was accepted by extremists in the South and was finally embodied in the Dred Scott decision of 1857. Abolitionists had meantime evolved a precisely contradictory theory. They asserted that the Constitution gave no warrant for property in man, except as held under state laws; that with this exception freedom was guaranteed to all; that Congress had no more right to make a slave than it had to make a king; and that it was the duty of Congress to maintain freedom in all the Territories. Extremists expressed the view that all past acts whereby slavery had been extended were unconstitutional and therefore void. Between these extreme conflicting views was every imaginable grade of opinion. The prevailing view of opponents of slavery, however, was in harmony with their past conduct and maintained that Congress had complete control over slavery in the Territories.