Under our federal system of government two sets of laws operate within the country, the laws of the constituent states and the laws of the central government. For lawyers there is the ever present question, which of them applies to a case: the law of a state, to be interpreted finally by the courts of the state; or national law--federal law, as it is usually called--of which the Supreme Court of the United States is the final arbiter?
Interstate and international matters, with which conflict of laws deals, involve national as well as state interests. In the United States it was perceived early that they should not be left to the uncontrolled discretion of the several states, and even the loose Articles of Confederation had a rudimentary full faith and credit clause. It was a major purpose of the Constitution of the United States to give to the nation increased control over these matters.
One of the shortcomings under the Articles of Confederation was that the nation lacked power to enforce its laws directly on the individual citizens, and was under the necessity of appealing to the states to take the desired action. A second shortcoming was that the states could and did discriminate against one another, particularly in trade and commerce. A third was the inadequacy of legal protection accorded the individual against government. These weaknesses were all dealt with by the Constitution either at once or shortly.
Elliott E. Cheatham,
Federal Control of Conflict of Laws,
6 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vlr/vol6/iss3/8