Recruinting in general is getting harder
https://www.npr.org/2023/01/18/1149855912/the-navy-has-raise...
My guess is that in a few years there will be a foreign legion in the French model (serve some years, gain citizenship)
Contrast that with my generation (late GenX). The single "big" war growing up was the first Iraq War. It was relatively popular and we "won" the war... the follow-on was no-fly enforcement, but minimal boots on the ground. And we grew up with parents deployed on a regular schedule to Germany or Korea, usually relatively comfortable places.
https://www.uscis.gov/military/naturalization-through-milita...
It's not exactly a foreign legion style thing but you can become a citizen via military service.
https://www.uscis.gov/military/naturalization-through-milita...
Arguably the Roman army always had foreigners, and it failed when it stopped trying to assimilate them and just treated them as mercenaries.