How did American politics move from regionalism (focus on a region, like South or North) to nationalism

Can a "good business" be an unethical business?
December 14, 2017
Economics of Environmental Quality
December 14, 2017

1. How did American politics move from regionalism (focus on a region, like South or North) to nationalism (American issues concern the nation, not just the region) in the period between 1865 and 1896?

2. In what way does populism influence our current-day politics? Please provide examples and make this a civilized discussion.