The adoption of an imperialist policy, which sought to increase American influence and territory abroad, was one significant shift in American foreign policy in the Pacific region at the end of the nineteenth century. The Philippines, Guam, Hawaii, and Puerto Rico were all acquired by the United States following the Spanish-American War in 1898, serving as examples of this policy.
Prior to this change in foreign policy, the United States had adopted a more isolationist stance and shunned participation in European colonialism and imperialism. However, the desire for expansion and influence outside of its borders was sparked by the nation's rising economic and military might as well as a perception of American exceptionalism.
This shift in policy was also a result of a growing acceptance of the doctrine of "Manifest Destiny," which held that it was the duty of the United States to enlarge its realm of influence and control across all of North America and beyond. American trade was seen to be expanded, American interests were protected, and American power was projected on the global stage through the annexation of new territories in the Pacific region.