The French Foreign Legion is open to anyone from any nation. After serving three years you are able to obtain a French citizenship. However, getting through the program is not as easy as it seems. Those in the legion are stripped of their identity and are given a new name. Once you enter training you give up who you are. Some describe it as being broken down mentally and physically. They also haze you which can make it difficult to quit.
Source: https://www.wearethemighty.com/history/french-foreign-legion-american-enlistee