What factors influenced American growth and expansion in the late nineteenth and early twentieth century?

Progressivism was the reform movement that ran from the late 19th century through the first decades of the 20th century, during which leading intellectuals and social reformers in the United States sought to address the economic, political, and cultural questions that had arisen in the context of the rapid changes brought with the Industrial Revolution and the growth of modern capitalism in America. The Progressives believed that these changes marked the end of the old order and required the creation of a new order appropriate for the new industrial age.