Im confused about how my great grandfather John James Nolan immigrated to the U.S. in 1916
From what I understand all the people that immigrated to the U.S. in 1916 were on ships; well at least the regular people, so I frantically searched google on the history of ships that brought people to the U.S. from Ireland, including the ones that arrived in Ellis Island, no luck in finding my great grandfather John James Nolan but then while doing some research on the history of Ireland it crossed my mind he immigrated to the U.S. during the Easter Rising, so out of curiosity I searched online the Irish Army Census records for the year 1916, Sure enough it seems that my great grandfather was part of the Easter Rising in the document I found while searching the Irish Army Census records, Im adding an attachment of the document, in the document it shows he is from the parish Killinagh, which is of course in county Cavan. Now the part that does not makes sense to me is that if my great grandfather John James Nolan was part of the Easter Rising then how would he have immigrated to the U.S. while being perhaps in the Irish Army and then later on join the U.S. military? Did dual citizenships existed back then between different countries?
Francis John Nolan