The principal commerce clause of the federal constitution, (Art. I, § 8, ¶ 3), is as follows: The Congress shall have power "to regulate commerce with foreign nations, and among the several states, and with the Indian tribes." (1) The necessity of such control with reference to foreign commerce is manifold and self-evident. It is essential in determining the relations of the general government to foreign countries, and in exercising supervision over navigation by vessels carrying the flag of the United States on the high seas and other public waters. (2) The necessity for federal regulation of interstate commerce arises from the fact that without such regulation freedom of commercial intercourse between residents of the different states on an equal basis would be impossible. (3) Commerce with the Indian tribes was put under the control of Congress, because those tribes were recognized as to some extent independent and self-governing bodies, existing within the limits of the United States, over which the national government asserted a form of protection, although the members of such tribes were not, as individuals, subjects of the United States. As to any forms of commerce not coming within one of these three classifications, the states are allowed to retain the power of control and regulation as effectually as though independent of each other and not subject to federal authority.