I will first quote from the opinion of the majority of the court:
Martial law can not arise from a threatened invasion. The necessity must be actual and present, the invasion real, such as effectually closes the courts and deposes the civil administration.
We see that martial law comes in only when actual war closes the courts and deposes the civil authority; but this bill, in time of peace, makes martial law operate as though we were in actual war, and becomes the _cause_ instead of the _consequence_ of the abrogation of civil authority. One more quotation:
It follows from what has been said on this subject that there are occasions when martial law can be properly applied. If in foreign invasion or civil war the courts are actually closed, and it is impossible to administer criminal justice according to law, _then_, on the theater of active military operations, where war really prevails, there is a necessity to furnish a substitute for the civil authority thus overthrown, to preserve the safety of the army and society; and as no power is left but the military, it is allowed to govern by martial rule until the laws can have their free course.
I now quote from the opinion of the minority of the court, delivered by Chief Justice Chase:
We by no means assert that Congress can establish and apply the laws of war where no war has been declared or exists. Where peace exists, the laws of peace must prevail.
This is sufficiently explicit. Peace exists in all the territory to which this bill applies. It asserts a power in Congress, in time of peace, to set aside the laws of peace and to substitute the laws of war. The minority, concurring with the majority, declares that Congress does not possess that power. Again, and, if possible, more emphatically, the Chief Justice, with remarkable clearness and condensation, sums up the whole matter as follows:
There are under the Constitution three kinds of military jurisdiction--one to be exercised both in peace and war; another to be exercised in time of foreign war without the boundaries of the United States, or in time of rebellion and civil war within States or districts occupied by rebels treated as belligerents; and a third to be exercised in time of invasion or insurrection within the limits of the United States, or during rebellion within the limits of the States maintaining adhesion to the National Government, when the public danger requires its exercise. The first of these may be called jurisdiction under military law, and is found in acts of Congress prescribing rules and articles of war or otherwise providing for the government of the national forces; the second may be distinguished as military government, superseding as far as may be deemed expedient the local law, and exercised by the military commander under the direction of the President, with the express or implied sanction of Congress; while the third may be denominated martial law proper, and is called into action by Congress, or temporarily, when the action of Congress can not be invited, and in the case of justifying or excusing peril, by the President, in times of insurrection or invasion or of civil or foreign war, within districts or localities where ordinary law no longer adequately secures public safety and private rights.