What ideas and interests motivated the united states to create an empire in the late nineteenth century?

There were numerous. For starters, they developed their fleets because it was believed that without a strong naval presence you cannot control trade routes or become even stronger. They were also inspired by the Manifest Destiny ideas that they should spread democracy worldwide and take down totalitarian regimes. They also believed that trading requires a drastic approach to foreign policy to ensure that your products are sold everywhere. There was also the idea of nationalism which started developing due to the widespread yellow press.

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