[nascarnation]

Military service in a foreign country is not an expatriating act if service is as a soldier who is not an officer, unless the foreign military is engaged in hostilities with the United States. Further, foreign military service usually does not cause loss of nationality since an intention to relinquish nationality normally is lacking. In adjudicating loss of nationality cases, the Department has established an administrative presumption that a person serving in the armed forces of a foreign state not engaged in hostilities against the United States does not have the intention to relinquish nationality.

https://travel.state.gov/content/travel/en/legal/travel-legal-considerations/Advice-about-Possible-Loss-of-US-Nationality-Dual-Nationality/Loss-US-Nationality-and-Foreign-Military-Service.html

[T.B. Yoits]

There's a reason the paperwork for such mercenaries is deceptive. You see a paycheck from Burisma Holdings before you see a direct paycheck from the Ukrainian Army.

They'll show up as "support", "trainers", or "advisors" when they're actively directing foreign troops, making them in effect Non-Commissioned Officers (NCOs) or Officers, both of which ARE expatriating acts.