Defense Primer: Legal Authorities for the Use of Military Forces Page: 2 of 2
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has also interpreted some military uses of force to fall
below the threshold of "hostilities" within the meaning of
Use of Military Forces to Execute
Under the Constitution, states retain the primary
responsibility and authority to provide for civil order and
the protection of their citizens' lives and property.
However, the Constitution provides that the federal
government is responsible for protecting the states against
invasion and insurrection, and, if the state legislature (or the
governor, if the legislature cannot be convened) requests it,
protection against "domestic Violence." While Congress is
also empowered to authorize the militia to be called forth to
execute federal law, historical precedent suggests that such
use was meant to be rare.
The Insurrection Act
Soon after Congress was first assembled under the
Constitution, it authorized the President to call out the
militia, initially to protect the frontier against "hostile
incursions of the Indians," and subsequently in cases of
invasion, insurrection, or obstruction of the laws.
Insurrections against state governments could be put down
under the act only if the state legislature applied for such
assistance. These provisions were quickly extended to allow
for the employment of the Armed Forces in domestic
circumstances where the law already provided the militia
could be employed. After the Civil War, Congress added a
new provision for the use of federal military forces for the
protection of civil rights.
The Insurrection Act has been invoked on dozens of
occasions through U.S. history, although its use since the
end of the 1960s civil rights disturbances has become
exceedingly rare. Its last invocation appears to have
occurred in 1992, when the acquittal of police officers on
charges of beating motorist Rodney King sparked rioting in
Los Angeles. Congress amended the statute in 2006 after
Hurricane Katrina raised concerns that the statutory
requirements impeded the military's ability to render
effective assistance amid the perceived breakdown of civil
law and order, but repealed that amendment the following
year after state governors objected to it.
The Posse Comitatus Act
The Posse Comitatus Act (PCA) outlaws the willful use of
any part of the Army or Air Force to execute the law unless
expressly authorized by the Constitution or an act of
Congress. The Navy and Marine Corps operate under
similar restrictions pursuant to regulations.
Whoever, except in cases and under circumstances
expressly authorized by the Constitution or Act of
Congress, willfully uses any part of the Army or the
Air Force as a posse comitatus or otherwise to
execute the laws shall be fined under this title or
imprisoned not more than two years, or both.
Defense Primer: Legal Authorities for the Use of Military Forces
The express statutory exceptions include legislation that
allows the President to use military force to suppress
insurrection or to enforce federal authority, and laws that
permit the Department of Defense to provide federal, state,
and local police with information, equipment, and
Case law indicates that "execution of the law" in violation
of the PCA occurs (1) when civilian law enforcement
officials make "direct active use" of military investigators;
or (2) when the use of military "pervades the activities" of
the civilian officials; or (3) when the military is used so as
to subject "citizens to the exercise of military power which
was regulatory, prescriptive, or compulsory in nature."
However, the PCA is not violated when the Armed Forces
conduct activities for a military purpose. Additionally, the
PCA does not apply to the National Guard unless it is
employed in federal service.
50 U.S.C. 1541-1548
10 U.S.C. 251-255 and 271-284
18 U.S.C. 1385
CRS Report RL3 1133, Declarations of War and Authorizations
for the Use of Military Force: Historical Background and Legal
Implications, by Jennifer K. Elsea and Matthew C. Weed
CRS Report R42699, The War Powers Resolution: Concepts and
Practice, by Matthew C. Weed
CRS Report R42738, Instances of Use of United States Armed
Forces Abroad, 1798-2017, by Barbara Salazar Torreon
CRS Report R41989, Congressional Authority to Limit Military
Operations, by Jennifer K. Elsea, Michael John Garcia, and
Thomas J. Nicola
CRS Report R42659, The Posse Comitatus Act and Related
Matters: The Use of the Military to Execute Civilian Law, by
Jennifer K. Elsea
Jennifer K. Elsea, firstname.lastname@example.org, 7-5466
18 U.S.C. 1385
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Elsea, Jennifer K. Defense Primer: Legal Authorities for the Use of Military Forces, report, November 13, 2018; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc1442981/m1/2/: accessed September 22, 2023), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.