Intel Slava often posts about various foreign mercenaries fighting on the Uke side, usually when they are killed. I’ve seen Americans (more than a handful), Netherlands, UK, Scandinavian countries, and others.
What idiots.
I remember when American mercenaries were fighting the Russians in Afghanistan (And elsewhere). There was even a magazine, “Soldier of Fortune” covering all the hot spots.
IIRC, there was a lot of action in Afghanistan at the time. American adrenaline junkies went there to join the Mujahedin (sp?) fighting against the Russian invaders.