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.