2010] NATURAL LAW AND SELF-DEFENSE 43
NATURAL LAW AND SELF-DEFENSE
MAJOR JOHN J. MERRIAM∗
There is in fact a true law—namely, right reason—which
is in accordance with nature, applies to all men, and is
unchangeable and eternal.1
If a man by the terrour of present death, be compelled to
doe a fact against the Law, he is totally Excused;
because no Law can oblige a man to abandon his own
The United States is currently engaged in combat and
counterinsurgency operations in Iraq and Afghanistan, with over 137,000
U.S. soldiers on the ground in those two countries alone.3 As troops have
been drawn down in Iraq, they have been shifted to Afghanistan based on
President Obama’s decision to surge up to 30,000 additional soldiers and
∗ Judge Advocate, U.S. Army. Presently assigned as the Group Judge Advocate, 10th
Special Forces Group (Airborne), Fort Carson, Colorado. LL.M., 2010, The Judge
Advocate General’s Legal Center and School, Charlottesville, Virginia; J.D., 2001, Case
Western Reserve University School of Law; B.A., 1996, University of Notre Dame.
Previous assignments include Brigade Judge Advocate, 12th Combat Aviation Brigade,
Ansbach, Germany; Trial Defense Counsel, Fort Lewis, Washington; Brigade Judge
Advocate, 1st Brigade, 25th Infantry Division, Fort Lewis, Washington and Mosul, Iraq;
Chief, International and Operational Law, I Corps, Fort Lewis, Washington;
Administrative Law Attorney, Fort Lewis, Washington. Member of the bar of Ohio. This
article was submitted in partial completion of the Master of Laws requirements of the
58th Judge Advocate Officer Graduate Course. The article received the Major General
George S. Prugh Award for Writing Excellence in International & Operational Law,
which is awarded by The Judge Advocate General’s Legal Center and School for the best
scholarly paper written in International & Operational Law.
1 MARCUS TULLIUS CICERO, DE RE PUBLICA bk. 3, quoted in Robert N. Wilkin, Cicero
and the Law of Nature, in ORIGINS OF THE NATURAL LAW 23 (Arthur L. Harding ed.,
2 THOMAS HOBBES, LEVIATHAN 345 (C.B. MacPherson ed., Penguin Classics 1985)
3 See BROOKINGS INST., IRAQ INDEX: TRACKING VARIABLES OF RECONSTRUCTION AND
SECURITY IN POST-SADDAM IRAQ 23 (2009), available at http://www.brookings.edu/~/
media/Files/Centers/Saban/Iraq%20Index/index.pdf (indicating a total of 47,000 U.S.
troops); BROOKINGS INST., AFGHANISTAN INDEX: TRACKING VARIABLES OF
RECONSTRUCTION AND SECURITY IN POST-9/11 AFGHANISTAN 10 (2009) [hereinafter
AFGHANISTAN INDEX], available at http://www.brookings.edu/~/media/Files/Programs/
FP/afghanistan%20index/index.pdf (indicating a total of 90,000 U.S. troops).
44 MILITARY LAW REVIEW [Vol. 206
Marines into Afghanistan.4 These warriors are committed to a complex
and ever-changing battlefield, in which identifying the enemy often
constitutes the chief obstacle to successfully engaging him. Under such
conditions, the primary rationale for the use of lethal force is quite often
self-defense. Self-defense as a form of self-help is universally recognized
as a legitimate basis for the use of force by states5 and their soldiers6
under international law. However, when, exactly, the right to self-
defense is triggered has been the subject of vigorous debate.7 The
concept of anticipatory self-defense—action taken in self-defense before
an “aggressor” strikes—has many critics, and even those who support its
validity disagree over the exact temporal limits of its use.8
Debate over the validity of anticipatory self-defense has raged for
decades, though the arguments were generally confined to the right of
states to engage in pre-emptive military action and did not necessarily
impact the immediate actions of soldiers on the battlefield. In 2005,
however, the United States changed the Standing Rules of Engagement
(SROE)9 that govern its soldiers in combat.10 While the SROE had
always authorized self-defense in response to an “imminent threat,” the
2005 SROE defined that term for the first time, stating that “imminent
does not necessarily mean immediate or instantaneous.”11 As a result, the
matter of the temporal boundaries surrounding anticipatory self-defense
now directly affects individual soldiers in combat.12 By defining
“imminent” in this way, the UnitedStates has effectively opened the door
to the use of force in self-defense against non-immediate threats.13
This article argues that the original basis for the right of self-defense
is the natural law and that the natural law requires that self-defense only
be used in response to an immediate threat.14 Consequently, the U.S.
4 AFGHANISTAN INDEX, supra note 3, at 10.
5 YORAM DINSTEIN, WAR, AGGRESSION, AND SELF-DEFENSE 175 (2005).
6 Commander Albert S. Janin, Engaging Civilian-Belligerents Leads to Self-
Defense/Protocol I Marriage, ARMY LAW, July 2007, at 82, 90 (arguing that “[t]he rights
of nations are delegated to their agents on the battlefield”).
7 See generally Sean D. Murphy, The Doctrine of Preemptive Self-Defense, 50 VILL. L.
REV. 699, 703–06 (2005).
9 CHAIRMAN OF THE JOINT CHIEFS OF STAFF, INSTR. 3121.01.B, STANDING RULES OF
ENGAGEMENT (13 June 2005) [hereinafter 2005 SROE].
10 See infra Part V.C.
14 See infra Part II.
2010] NATURAL LAW AND SELF-DEFENSE 45
SROE are no longer in accord with natural law, which may result in
friction in two forms.15 First, because U.S. domestic law on self-defense
draws heavily on the natural law,16 the SROE may now allow actions that
U.S. law does not.17 Secondly, natural law consists of principles that are
universally understood by all rational beings,18 but the blurring of the
definition of imminence has created enormous uncertainty over what
actions may trigger a lethal response by U.S. soldiers in Iraq and
Afghanistan, especially among civilians.19 This uncertainty, in turn,
undermines the perceived legitimacy of U.S. actions and hinders
cooperation between U.S. forces and civilians.
Part II of this article will trace the origins of natural law theory from
the Romans through Thomas Aquinas and Hugo Grotius, and will show
that the natural law allows for the use of force in self-defense only in
response to an immediate threat.20 Part III will then explain the influence
of natural law over international law, including the Caroline Doctrine
and Article 51 of the U.N. Charter, and will argue that both Caroline and
Article 51 adhere to a natural law standard and, consequently, require an
immediate threat.21 Part IV will explore the influence of natural law on
the domestic law of the United States and will show that U.S. law also
requires the existence of an immediate threat before self-defense is
allowed.22 In Part V, this article will demonstrate how these two strains
of law—international and domestic—are synthesized in the Rules of
Engagement and will explain how the 2005 changes to the SROE
represented a dramatic departure from the imminent threat standard
articulated by natural law.23 Finally, Part VI will explore the friction
caused by this departure from natural law and the expected consequences
of it.24 The article will conclude by arguing that the United States should
abandon its expanded definition of imminence and adhere to a stricter
requirement of immediacy.25
15 See infra Part VI.
16 See infra Parts IV & V.
17 See infra Part VI.
18 See infra Part II.
19 See infra Part VI.
20 See infra Part II.
21 See infra Part III.
22 See infra Part IV.
23 See infra Part V.
24 See infra Part VI.
25 See infra Part VII.