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 interest 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 the 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. [The remark of the author, that 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, which is more strongly expressed in the original, is erroneous and calculated to mislead on a point of some importance. By the grant of power to the courts of the United States to decide certain cases, the powers of the state courts are not suspended, but are exercised concurrently, subject to an appeal to the courts of the United States. But if the decision of the state court is _in favor_ of the right, title, or privilege claimed under the constitution, a treaty, or under a law of congress, no appeal lies to the federal courts. The appeal is given only when the decision _is against_ the claimant under the treaty or law. See 3d Cranch, 268. 1 Wheaton, 304.--_American Editor._] Thus the jurisdiction of the general 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.[149] 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.[150]