During the period 1781-88, an agreement called the Articles of Confederation governed relations among the 13 states. It established a weak national Congress and left most authority with the states. The Articles made no provision for a federal judiciary, save a maritime court, although each state was enjoined to honor (afford "full faith and credit" to) the rulings of the others' courts.

The drafting and ratification of the Constitution reflected a growing consensus that the federal government needed to be strengthened. The legal system was one of the areas where this was done. Most significant was the "supremacy clause," found in Article VI:

This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.

This paragraph established the first principle of American law: Where the federal Constitution speaks, no state may contradict it. Left unclear was how this prohibition might apply to the federal government itself, and the role of the individual state legal systems in areas not expressly addressed by the new Constitution. Amendments would supply part of the answer, history still more, but even today Americans continue to wrestle with the precise demarcations between the federal and state domains.