The concept of the "frontier" was a force of colonization and genocide of indigenous people in what is now known as the United States throughout the 18th and 19th centuries. Manifest Destiny was the driving concept that supported the westward colonial expansion of white settlers. The process of westward expansion is typically celebrated as a reflection of American individualism and ruggedness. Movies and films celebrate the raiding and massacring of indigenous tribes as white settlers forced their way westward, destroying the homelands of many tribes. When the "frontier" was officially closed in 1890, the United States immediately began turning into an imperialist power that sought to colonize and control other nations around the world. The Spanish-American War, particularly, ignited this imperialism across the world.

When the U.S. Census Bureau announced the closing of the frontier in 1890, American foreign policy made a fateful shift. Politicians, intellectuals and industrialists began to wonder what the guiding force in expansion would be. The frontier was significant because it allowed our national character to shift from being European to being American. We had to invent new ways of solving problems, and these solutions began changing our national character into a rugged, individualistic and liberty-loving people.

Frederick Jackson Turner wrote that the closing of the frontier meant that the motor for American change had to shift, and many business magnates in Washington began casting an eye towards the Pacific. Trade opportunities, territorial acquisitions and the potential for growth all lay there.

So, the most important result of the closing of the frontier was that American began moving towards becoming an imperialist nation.