The powers delegated by the proposed Constitution to the Federal Government, are few and defined. Those which are to remain in the State Governments are numerous and indefinite. The former will be exercised principally on external objects, as war, peace, negotiation, and foreign commerce; with which last the power of taxation will for the most part be connected. The powers reserved to the several States will extend to all the objects, which, in the ordinary course of affairs, concern the lives, liberties and properties of the people; and the internal order, improvement, and prosperity of the State.
The operations of the Federal Government will be most extensive and important in times of war and danger; those of the State Governments, in times of peace and security. As the former periods will probably bear a small proportion to the latter, the State Governments will here enjoy another advantage over the Federal Government. The more adequate indeed the federal powers may be rendered to the national defense, the less frequent will be those scenes of danger which might favour their ascendency over the governments of the particular States.
Source: Madison, James. Federalist Papers No. 45.