U.S. History How did the United States emerge as a world power in the early 1900's?

The United States emerged as a world power from the economic boom it experienced after WWI. The United States had already experienced an immense strengthening as an imperialist, militarized world power after its victory in the Spanish-American War in 1898 and its colonial, imperialist acquisition of Puerto Rico, the Philippines, and Guam as a result. Because of the Industrial Revolution, the United States was able to be a part of a massive war economy that led to a huge economic boom for the United States. The United States displayed undeniable military strength during WWI and enjoyed great economic and military strength throughout the 1920s, until the the Great Depression hit. This was a result of the strength of the U.S. military and from the U.S. loaning billions of dollars to the Allies. Once the war was resolved, the United States emerged as a world power who was able to begin the process of collecting debts from and holding power over several European nations.

There were a number of factors that contributed to the United States emerging as a world power in the early 1900's.  Industrialism and manufacturing are very important to American international prestige and power. The United States had a vast variety and quantity of natural resources that allowed successful industry to take root in the Northeast.  Due to a relaxed immigration policy, the fulfilling the labor needs of a growing industrial and urban economy was not an issue.  Industrialism created wealth and allowed for the establishment of a technologically sound military instrument. 
The United States was also establishing itself as a world power because of its expansion.  Having reached the West coast through expansion, America looked outside of the continental United States to exert its power and utilize resources of foreign peoples.  The victory in the Spanish-American War, and later in the Philippine-American War allowed the United States to expand into the Pacific and the Caribbean.  This was achieved through a powerful military and a strong desire to use that powerful military.  
https://americanhistory.si.edu/presidency/timeline/pres_era/3_657.html