This section embraces three classes of cases. The first, those in which a State court should decide a law or treaty of the United States to be void, either because it violated the Constitution of the United States, or for any other reason. Ought there not in such cases to be an appeal to the Supreme Court of the United States? Without such an appeal, the General Government might be obliged to behold its own laws and its solemn treaties annulled by the judiciary of every State in the Union, without the power of redress. The second class of cases is of a different character. It embraces those causes in which the validity of State laws is contested, upon the principle that they violate the Constitution, the laws, or the treaties of the United States, and have, therefore, been enacted in opposition to the authority of the “supreme law of the land.” Cases of this description have been of frequent occurrence. It has often been drawn into question before the State courts, whether State laws did or did not violate the Constitution of the United States. Is it not then essential to the preservation of the General Government, that the Supreme Court of the United States should possess the power of reviewing the judgments of State courts in all cases wherein they have established the validity of a State law in opposition to the Constitution and laws of the United States? The third class differs essentially from each of the two first. In the cases embraced by it, neither the validity of acts of Congress, nor of treaties, nor of State laws is called in question. This clause of the 25th section merely confers upon the Supreme Court the appellate jurisdiction of construing the Constitution, laws, and treaties of the United States, when their protection has been invoked by parties to suits before the State courts, and has been denied by their decision. Without the exercise of this power, in cases originating in the State courts, the Constitution, laws, and treaties of the United States would be left to be finally construed and executed by a judicial power, over which Congress has no control.