Question - What is a reason Nationalism has become a movement across the world in the modern era?

answer; andrew jackson approved nullification by signing it into law,and john calhoun opposed it saying it was unconstitutional;

the right answer for the question that is being asked and shown above is that: "their policy of "divide and rule" pitted political groups against each other to keep any one group from becoming too powerful.  " the  participant in european imperialism is being described below is that  their policy of "divide and rule" pitted political groups against each other to keep any one group from becoming too powerful.