The United States of the 19th century and the United States of the 20th century differ a great deal. In most of the 19th century, the US was isolationist and did not get involved much in the affairs of the world. However, by the start of the 20th century, the US began to get involved a greater amount in world affairs. The Spanish-American War (1898) established the United States as a world power and caused the US to follow the path of imperialism.
The Treaty of Paris in 1898, involving Spain and the United States, granted Cuba its freedom and also gave the US the territory-islands of Puerto Rico in the Caribbean Sea and Guam in the Pacific Ocean. The US, as promised in the Teller Amendment, allowed Cuba to be free in 1902, but it kept its sphere of influence with the Platt Amendment, which stated that Cuba could not impair its independence by treaty, the US could intervene with troops if necessary, and the US could use Guantanamo Bay as a naval station.
With the United States now owning territories in the Caribbean and Pacific, it allowed for stronger naval presence and easier trade (due to coal stations on these islands). All these factors led to the establishing the US as a world power.
During the Spanish-American War, the US navy, led by General Dewey, captured the strategically located and sugar-rich Philippine islands in the Pacific. President McKinley, after much difficult deliberation, decided that the United States would keep these islands as territories, despite his claims of not being an imperialist. The United States now began its process of "Americanization" on the brown people of the Philippines. This started a whole new chapter for the United States as an imperialistic nation. It now had a...