Whenever the laws of the United States are attacked, or whenever they are resorted to in self-defence, the Federal courts must be appealed to. Thus the jurisdiction of the tribunals of the Union extends and narrows its limits exactly in the same ratio as the sovereignty of the Union augments or decreases. We have shown that the principal aim of the legislators of 1789 was to divide the sovereign authority into two parts. In the one they placed the control of all the general interests of the Union, in the other the control of the special interests of its component States. Their chief solicitude was to arm the Federal Government with sufficient power to enable it to resist, within its sphere, the encroachments of the several States. As for these communities, the principle of independence within certain limits of their own was adopted in their behalf; and they were concealed from the inspection, and protected from the control, of the central Government. In speaking of the division of authority, I observed that this latter principle had not always been held sacred, since the States are prevented from passing certain laws which apparently belong to their own particular sphere of interest. When a State of the Union passes a law of this kind, the citizens who are injured by its execution can appeal to the Federal courts. Thus the jurisdiction of the Federal courts extends not only to all the cases which arise under the laws of the Union, but also to those which arise under laws made by the several States in opposition to the Constitution. The States are prohibited from making ex post facto laws in criminal cases, and any person condemned by virtue of a law of this kind can appeal to the judicial power of the Union. The States are likewise prohibited from making laws which may have a tendency to impair the obligations of contracts. *i If a citizen thinks that an obligation of this kind is impaired by a law passed in his State, he may refuse to obey it, and may appeal to the Federal courts. *j i [ It is perfectly clear, says Mr. Story (“Commentaries,” p. 503, or in the large edition Section 1379), that any law which enlarges, abridges, or in any manner changes the intention of the parties, resulting from the stipulations in the contract, necessarily impairs it. He gives in the same place a very long and careful definition of what is understood by a contract in Federal jurisprudence. A grant made by the State to a private individual, and accepted by him, is a contract, and cannot be revoked by any future law. A charter granted by the State to a company is a contract, and equally binding to the State as to the grantee. The clause of the Constitution here referred to insures, therefore, the existence of a great part of acquired rights, but not of all. Property may legally be held, though it may not have passed into the possessor’s hands by means of a contract; and its possession is an acquired right, not guaranteed by the Federal Constitution.]