since he is far from the only person to overuse the term (I inhabit a whole thread devoted to its use and overuse );

but why do we too often directly jump to this question:

from Rifleman
Did the Gurkha commit a war crime? I understand he displayed cultural insensitivity and he may have violated his commander's policy. But did he commit a war crime? I don't know, but if he did I won't condone it.
Not every breach of the various conventions is a "war crime" - most breaches are not.

Our understanding is not helped by 1975 (rev.) FM 27-10, which is otherwise usually accurate for its vintage, which lays down this "blackletter":

499. War Crimes
The term "war crime" is the technical expression for a violation of the law of war by any person or persons, military or civilian. Every violation of the law of war is a war crime.
That "blackletter" is simply too simplistic and can lead people legally astray.

The 2010 Operational Law Handbook provides us with a 5-COAs approach:

XVI. REMEDIES FOR VIOLATIONS OF THE LAW OF WAR

A. U.S. Military and Civilian Criminal Jurisdiction

1. The historic practice of the military services is to charge members of the U.S. military who commit offenses regarded as a “war crime” under existing, enumerated articles of the UCMJ.[165]

2. In the case of other persons subject to trial by general courts-martial for violating the laws of war[166] the charge shall be “Violation of the Laws of War” rather than a specific UCMJ article.

3. The War Crimes Act of 1997[167] provides federal courts with jurisdiction to prosecute any person inside or outside the U.S. for war crimes where a U.S. national or member of the armed forces is involved as an accused or as a victim.

4. “War Crimes” are defined in the War Crimes Act as: (1) grave breaches as defined in the Geneva Conventions of 1949 and any Protocol thereto to which the U.S. is a party; (2) violations of Articles 23, 25, 27, 28 of the Annex to the Hague Convention IV; (3) violations of Common Article 3 of the Geneva Conventions of 1949 and any Protocol thereto to which the U.S. is a party and deals with a non-international armed conflict; (4) violations of provisions of Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-Traps & Other devices (Protocol II as amended May, 1996) when the U.S. is a party to such Protocol and the violator willfully kills or causes serious injury to civilians.

5. U.S. policy on application of the LOW is stated in DoD Directive 2311.01E (9 May 2006): “It is DoD policy that … [m]embers of the DoD Components [including U.S. civilians and contractors assigned to or accompanying the armed forces] comply with the LOW during all armed conflicts, however such conflicts are characterized, and in all other military operations.”

165 FM 27-10, para. 507.
166 UCMJ, art. 18.
167 18 U.S.C. § 2441. [JMM Note: "war crimes" violations of Common Article 3 are more carefully defined in the statute and by court decisions than 2010 OLH states - again, not all CA3 violations are "war crimes"]
A less legalistic approach appears in a posting at Free Republic from another denizen of our SWC zoo (Polarbear1605), Laws of War to Rules of Law or the Old Switch-A-Roo!, where The Great Furry One first notes:

The UCMJ is a uniquely military judicial system because when you look at the UCMJ Articles, you find not only civilian or Rules of Law (common law) charges like Murder, Robbery and Larceny but also military charges like Desertion, Absent without Leave and Disrespect to a Superior Commissioned Officer. There are some 60 punitive articles in the UCMJ and one of the puzzling features of the UCMJ is that there are no specific articles for war crimes.
Da Bear gets into the guts of the "war crimes" problem with this:

These ROEs are clearly based on the three principles of the Laws of War; military necessity, proportionality and distinction. These Law of War principles are exactly what Soldiers and Marines in combat are trained not only to base their tactical decisions on but also they are ordered and continually reminded to follow.

Now here is the issue, if our servicemen are operating in combat in a foreign country under the Laws of War ROE, why are they being charged with murder instead of violating one or more of the principles of the Laws of War. Another way to say this is why are we charging our warriors with murder on the battle field instead of violating the combat ROE rules and regulations established for combat operations?

Each service has its own War Crimes directives. As an example, let’s look at Marine Corps MCRP (Marine Corps Reference Publication) 4-11.8B, War Crimes. This publication’s interesting part is that it maps war crimes to UCMJ articles. For example; “The willful killing, torture or inhuman treatment of individuals protected by the Geneva Conventions” which is a violation of military necessity, maps to the UCMJ Articles of: Article 93 Cruelty and Maltreatment Article 118 Murder Article 119 Manslaughter Article 120 Rape and Carnal Knowledge Article 122 Robbery Article 124 Maiming Article 128 Assault Article 134 General Article (indecent assault, negligent homicide)

The Manual for Courts-Martial (MCM) list the “elements of proof” for each of these punitive Articles. The elements of proof “are the specifics of the offense. In order to support a finding of "guilty," the government must prove each and every element of the offense, beyond a reasonable doubt”. Murder, for example, has the following elements of proof (according to the MCM):

“ Premeditated murder. (a) That a certain named or described person is dead; (b) That the death resulted from the act or omission of the accused; (c) That the killing was unlawful; and (d) That, at the time of the killing, the accused had a premeditated design to kill.”

Another way to state these elements of proof in layman terms: (a) You need to prove you have a dead body; (b) You need to prove who pulled the trigger; (c) It was not self defense (only rules of law I know to justify a dead body); and (d) You need to prove beyond a reasonable doubt the accused intended to kill the victim.

Notice that the MCM elements of proof make no mention of the Laws of War principles of military necessity, proportionality or distinction.
Great post by the White Bear, including his suggested script for a TV “Law and Order“ series.

Besides the unique concepts of military necessity, proportionality or distinction, the Laws of War also are based on reciprocity. True, they can chug along on autopilot for a while; but if reciprocity is lacking, they eventually develop disconnects.

Lack of reciprocity comes from various causes - e.g., different cultures, different legal systems. Or, it can come about because of what PB1605 terms “Strategic Legalism”:

The definition of Strategic Legalism is “the use of law or legal arguments to further larger policy objectives, irrespective of facts or laws”. .....

Strategic Legalism is a political maneuver that has existed for a long while. Peter Maguire, who defined the term, credits the maneuver to Secretary of War Elihu Root (1845 – 1937) one of the first US Government lawyer-politician bureaucrats. The interesting story that Peter Maguire tells as one of the first examples of Strategic Legalism, centers on USMC Major Littleton Tazewell Waller and his court martial that took place during the Philippine American War (1899-1902).

Major Waller successfully defended himself using the existing Laws of War despite the widespread sensational press accusations of murder. The Major’s successful defense kept his career intact. He would later be considered as one of two candidates for the Marine Commandant; however, the other candidate would be selected.
How should one class the beheading videos (having watched a few) in terms of reciprocity and the reasons for them ? I expect that is very much in the eyes of the beholder. In my own eyes, comparing them to what the Gurk did (based on our limited facts) suggests that he was guilty of a breach of etiquette.

Regards

Mike