The idea of citizenship has changed throughout history because citizenship has been reshaped by immigration and the growth of population. In the past citizenship was determined moreso by the place you were born. For instance people born in Athens, or ancient Rome was considered citizens of that country. Now , especially in modern U.S.A citizenship can be earned and worked for. For instance the immigrants that come from overseas and foreign countries, they can come to America and be a citizen within a few years.
