Apparently, it happened around 2000.
* Marines get angry and insulted if you refer to them as "soldiers". They're Marines (and it had BETTER be capitalized).
* Members of the USAF were historically "Airmen", which became problematic when women were allowed to join. Its official solution was to use terms like "Enlisted", "Officers", and "Pilots". As a practical matter, the USAF doesn't want you unless you have a college degree, which almost automatically qualifies you to become a NCO after basic training, so you can *almost* generalize "heterogenous group of Air Force servicemembers" AS "Officers", especially anywhere near a combat zone (where, by definition, everyone has completed basic training).
In Iraq, and particularly in Afghanistan, service members tended to serve in mixed groups (though their living quarters were extraordinarily non-equal, to the point where USAF personnel living in modular buildings that could have almost passed for an Ikea showroom display on the inside felt bad when they found out the soldiers & Marines they worked with daily were sleeping on cots in tents & shitting into literal latrine holes), so any attack was likely to involve members of multiple branches. Plus, for the first time, lots of women were dying as well.
As I understand it, the present AP style guide rules are something like this:
* One member of the armed services is NEVER "a troop". If their service is unknown, they're a "servicemember" or "member of the (US) Armed Forces".
* When referring to two or more servicemembers, every effort should be made to identify them using the most specific gender-neutral collective noun available (ex: soldiers, sailors, Marines, pilots)
* Heterogenous groups can be referred to as either "servicemembers" or "troops", but "servicemember" is preferred in all contexts besides headlines (where brevity is of the essence).
The above notwithstanding... journalistic writing standards have deteriorated badly over the past decade. In the past, newspapers had Editors who ruled with an iron fist, proofread everything (either personally, or via a trusted delegate who answered to them directly), and harshly humiliated & punished those who made stylistic errors. Now, half the time, articles just get scored by AI. If the AI approves, it goes to press as-is. Otherwise, the journalist might appeal to his/her editor for an override... but today, Editors are rarely the all-powerful dictators (with authority to hire, fire, and determine the wording and content of news articles) they used to be. More often than not, they themselves are outsourced to a pool, and spend their day proofreading articles destined for a half-dozen newspapers, and literally don't have TIME to scrutinize and rewrite most of what passes through their workflow.
