Not all are Citizens: Each and Every one is a US Citizen OR a legal permanent immigrant, physically living in the United States, with a green card; you must be prior to enlistment.
Dude who cares.
US citizens may join the French Foreign Legion. Iran has peculiar citizenship laws which may not recognize a child born of Iranian parents (whether still Iranian citizens or naturalised US citizens) as a US citizen, and will require that child to perform compulsory military service when he reaches military age. However, most military forces of the world are not as prone to accepting foreign volunteers as the US military is.
Yes, an individual must be a current US Citizen to become an Officer in the US Military.
US Citizens facing the military draft.
Really depends, if both or one of the parents are US Citizens then yes regardless if the birth occurs on a military base in the US or outside the US. Now when it comes to the birth of a person with parents not currently US Citizens then it depends on the current laws within the US and that State at the time of birth.
Some military applications can be used by US civilians. Drones created by the US military can used by US citizens in some cases. Although it is unusual it is done.
Many returning veterans experienced rejection from their fellow US citizens, and US military morale suffered because of this experience.
Not necessarily. There are legal residents who are not US citizens serving in the US military. However, it will lead to citizenship with honorable service.
Yes, foreign citizens can serve in the US military, pending some criteria.
how many are buried in military cemeteries in the US?
No. Aside from the Brigade of Ghurkas, the British military accepts only citizens of the United Kingdom, Commonwealth countries (or countries which were in the Commonwealth at the time of the recruit's birth), and the Republic of Ireland. The USA is none of these, thus, US citizens are ineligible to enlist in the British military.
No They were citizens when the served in the military