Question

How did the USs foreign policies from 1870-1910 become more imperialistic?

Answer 1

By the 1890's Americans were sick and tired of their 1870 and prior image of being just backwoods farmers staying at home from the world. Americans in the 1890's were conscious of the great power of American industry, wealth, inventions, natural resources and wanted to take their place among the great powers of the world. They were aware of all the great progress America had made in every field. 

A new political movement the progressives wanted even more progress and aimed at the future to make America 'great'. This was the motivation for the new foreign policy. Examples: kicking Spain out and taking Cuba,(1898), buying Panama and building the American Panama Canal there (1904). President Theodore Roosevelt building the 1st mighty US Navy (1901-1909).