Can a former us service member join a foreign militaries?

If they'll accept foreign volunteers, yes. Offhand, I know the Israeli Mahal and French Foreign Legion do, but most militaries do not accept foreigners into their ranks.
In another instance of a similar question being asked, it was answered that one might lose their US citizenship status if they serve a foreign government which the US is at odds with. In reality, you will lose your citizenship, regardless of the status of relations between the US and that country.
If they'll accept foreign volunteers, yes. Offhand, I know the Israeli Mahal and French Foreign Legion do, but most militaries do not accept foreigners into their ranks.
In another instance of a similar question being asked, it was answered that one might lose their US citizenship status if they serve a foreign government which the US is at odds with. In reality, you will lose your citizenship, regardless of the status of relations between the US and that country.