Why was Eamon de Valera not executed after the Easter Rising?

Eamon de Valera was not executed by British authorities following the 1916 Easter Rising primarily because of his American birth.1

While 15 other leaders of the rebellion were court-martialed and executed, de Valera—who had commanded an occupied building and was the last commander to surrender—was instead sentenced to penal servitude. His status as a survivor of the uprising, combined with his role as a senior commander, contributed significantly to his subsequent political prominence and popularity in Ireland.123