Clearly, the existence of "war" and "armed conflict" must be determined for legal purposes (triggering of Conventions and various statutes) and for many derivative purposes (e.g., ROEs, RUFs, etc.).

The question is: for what purposes, other than legal and legal derivatives, do we need to define war (armed conflict); and how do those definitions differ from the legal construct ?

This question is generated by Steve Metz's Conference Brief (post on p.2).

For legal purposes in the US, the existence of "war" and "armed conflict" can be determined easily if we have either a formal declaration of war or an AUMF. Some uncertainly can exist if Congress has not yet acted and the Executive is acting under interim CinC authority. See below under line.

Except for legal definitions and practices, this and other discussions here about "war" seem to go around in circles. Discussions of "warfare", however, seem to be much more focused, even though they may be marked by intense disageements as to strategy, tactics, etc.

--------------------------
Declarations of War & AUMFs

Formal declarations of war were going out of style when the Constitution was drafted. James Kent (a noted NY judge, as well as a scholar), in Kent's Commentaries from 1826, made it perfectly clear that the Constitution did not require a formal declaration of war; but it did require a joint act of Congress:

LECTURE III. OF THE DECLARATION, AND OTHER ABLY MEASURES OF A STATE OF WAR.
....
2. Declaration of War.
....
But though a solemn declaration, or previous notice to the enemy, be now laid aside, it is essential that some formal public act, proceeding directly from the competent source, should announce to the people at home their new relations and duties growing out of a state of war, and which should equally apprise neutral nations of the fact, to enable them to conform their conduct to the rights belonging to the new state of things. War, says Vattel, is at present published and declared by manifestoes. Such an official act operates from its date to legalize all hostile acts, in like manner as a treaty of peace operates from its date to annul them. As war cannot lawfully be commenced on the part of the United States without an act of Congress, such an act is, of course, a formal official notice to all the world, and equivalent to the most solemn declaration.
Thus, there must be at least an AUMF act by Congress, which may be short of a formal declaration of war.

Kent illustrates that by examples from the times before and after the Constitution was adopted (footnotes omitted below - see full text at link above for context):

Since the time of Bynkershoek, it has become settled by the practice of Europe that war may lawfully exist by a declaration which is unilateral only, or without a declaration on either side. It may begin with mutual hostilities. After the peace of Versailles, in 1763, formal declarations of war of any kind seem to have been discontinued, and all the necessary and legitimate consequences of war flow at once from a state of public hostilities, duly recognized and explicitly announced by a domestic manifesto or state paper.

In the war between England and France, in 1T78, the first public act on the part of the English government was recalling its minister; and that single act was considered by France as a breach of the peace between the two countries. There was no other declaration of war, though each government afterwards published a manifesto in vindication of its claims and conduct. The same thing may be said of the war which broke out in 1793, and again in 1803; and, indeed, in the war of 1756, though a solemn and formal declaration of war, in the ancient style, was made in June, 1756, vigorous hostilities had been carried on between England and France for a year preceding.

In the war declared by the United States against England, in 1812, hostilities were immediately commenced on our part as soon as the act of Congress was passed, without waiting to communicate to the English government any notice of our intentions.
Formal declarations of war were somewhat revived by the Hague Conventions; but again fell into disuse after WWII.

Drawing the "Armed Conflict" Line

Some problems exist in the legal arena where the President acts unilaterally. It illustrates an instance from Kosovo where the lawyer-politicians at the "highest levels" did not measure their statements according to the legal norm.

From CLAMO's, LL Kosovo (pp. 61-62 pdf) (link here):

Both prior to and during the early days of the air campaign, disagreement existed within U.S. and NATO political and legal circles over whether or not LOAC applied to Operation Allied Force.[5] Because LOAC applies to international armed conflicts,[6] the precise legal issue was whether Operation Allied Force constituted an international armed conflict. It also seems apparent that political concerns entered the calculation.[7]

The debate proved more than academic when Yugoslav forces captured three U.S. soldiers conducting a security patrol along the border between the FRY and the former Yugoslav Republic of Macedonia (FYROM) on 31 March 1999, one week after NATO forces had dropped the first bombs of Allied Force.[8] At issue was the soldiers' legal status: were they prisoners of war entitled to full Geneva Convention[9] protections (as would be the case if LOAC applied); were they "detainees" entitled to some lesser status;[10] were they common criminals under host nation law; or were they something else?

The immediate U.S. political response was that the soldiers had been "illegally abducted."[11] This position quickly evolved into a curious amalgam of prisoner of war language mixed in with demands for immediate return of the soldiers (although prisoner of war status affords protections under international law, it also allows the detaining power to hold the prisoner until the end of the conflict).[12]

The ultimate U.S. position was that LOAC applied to Operation Allied Force and, accordingly, that the soldiers were prisoners of war.[13] However, by not presenting an early, united front on the status of the captured soldiers, equivocation within U.S. policy channels potentially placed the soldiers in harm's way. For example, the Serbs might have agreed with early U.S. statements that made no mention of prisoner of war status, thereby concluded that the soldiers did not have combatant immunity, and then tried the soldiers for domestic crimes.[14]

5. [JMM: very long footnote on jus ad bellum omitted; cited in note 5 and below, Major Geoffrey S. Corn & Major Michael L. Smidt, "To Be or Not to Be, That is the Question:" Contemporary Military Operations and the Status of Captured Personnel, ARMY LAW., June 1999, p.1 et seq.]

6 Common Article 2 of the Four Geneva Conventions of 1949 states that "the present Convention shall apply to all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties." Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field, Aug. 12, 1949, art. 2-3; Geneva Convention for the Amelioration of the Condition of Wounded, Sick, and Shipwrecked Members at Sea, Aug. 12, 1949, art. 2-3; Geneva Convention Relative to the Treatment of Prisoners of War, Aug. 12, 1949, art. 2-3; Geneva Convention Relative to the Treatment of Civilian Persons in Time of War, Aug. 12, 1949, art. 2-3.

7 See Kosovo AAR, supra note 5, at 257, 261.

8 For a detailed discussion of this incident and an analysis of the status of captured personnel in modern military operations, see Corn & Smidt, supra note 5, at 1.

9 Specifically, the Geneva Convention Relative to the Treatment of Prisoners of War, supra note 6.

10 The initial NATO guidance was that "detainee" would be the appropriate term for a captured member of NATO forces. See Kosovo AAR [CLAMO, Kosovo After Action Review Conference (12-14 June 2000); Transcript, note 5 of LL Kosovo] at 265.

11 The phrase was used by both President Clinton and Secretary of Defense Cohen. See Guy Dinmore & Joan Biskupic, Yugoslavia Opens Case Against 3 American Soldiers, WASH. POST, Apr. 3, 1999, at A11.

12 Department of State Spokesman James Rubin, at a press briefing held the day after the soldiers' capture, used a confusing mixture of terms, asserting that the soldiers were at once prisoners of war entitled to Geneva protections and "illegal detainees" who should be immediately released. James P. Rubin, U.S. Dep't of State Daily Press Briefing (Apr. 1, 1999).

13 On the same day that Mr. Rubin made his confusing comments, Department of Defense Spokesman Kenneth Bacon articulated what soon became the official U.S. government position: "We consider them to be [prisoners of war]. . . . By international law the Geneva Convention applies to all periods of hostilities . . . . [T]he government has decided that the Geneva Convention applies." Kenneth H. Bacon, Off. of the Ass't Sec'y of Defense (Public Affairs), Dep't of Defense News Briefing (Apr. 1, 1999). Interestingly, despite the conclusion that the soldiers were prisoners of war and thus could be kept until repatriated at the end of the conflict, the Reverend Jesse Jackson was widely credited with securing the soldiers' 2 May 1999 release as a result of the private religious delegation that he led to Serbia. ....

14 See Corn & Smidt, supra note 5, at 14-18.
An educational trip into why politicians should often shut up.

Regards

Mike