The provision of the federal constitution last above referred to, so far as it relates to the protection of the state governments, involves protection, not only against invasion, but also against domestic violence. As to invasion, no action of the state invoking federal protection is necessary; an invasion of a state is also an invasion of the United States, and would be a proper ground for the exercise of the federal executive power, involving the use of the military and naval forces (see above, § 130). In case of domestic violence against a state government the federal government is authorized to act only on application of the state legislature, if in session, or the executive when the legislature cannot be convened. It is provided by statute that this application be made to the president and that he may call out the militia of other states if a military force is necessary, and it is evidently implied that he may make use of any of the military and naval forces of the United States in the exercise of his discretion (see above, § 131).

The express denial to the states of the power to grant titles of nobility (Const. Art. I, § 10, ¶ 1) should properly be regarded as a provision for the preservation of a republican form of government, and the similar restriction on the power of the United States (Const. Art. I, § 9, ¶ 8) was undoubtedly intended to have the same effect in the preservation of a republican form for the federal government. These provisions are self-executing, and any attempted grant of such titles by the federal or a state government would be void because unconstitutional.