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 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
cannot 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.

We think that the power of Congress in such times and in such
localities to authorize trials for crimes against the security
and safety of the national forces may be derived from its
constitutional authority to raise and support armies and to
declare war, if not from its constitutional authority to
provide for governing the national forces.[Footnote: _Ex
parte_ Milligan, 4 Wallace's Reports, 141.]