After the Spanish-American War in 1898, the United States emerged as a world power with overseas territories and interests to protect. The United States' foreign policy shifted towards imperialism and expansion, as demonstrated by President Theodore Roosevelt's "Big Stick" policy and the Roosevelt Corollary to the Monroe Doctrine. The Big Stick policy was an aggressive foreign policy strategy that emphasized the use of military force to assert American interests and power abroad. The Roosevelt Corollary to the Monroe Doctrine, on the other hand, stated that the United States had the right to intervene in the affairs of other countries in the Western Hemisphere to maintain stability and protect American interests.
The Second Industrial Revolution also played a role in shaping foreign policy, as the United States needed new markets for its goods and resources to fuel its expanding industries. This led to a policy of economic expansion and the acquisition of overseas territories and markets, such as the annexation of Hawaii, Puerto Rico, and Guam. The foreign policy during this period was marked by a belief in American exceptionalism, the idea that the United States had a special role to play in the world and that it had a moral obligation to spread its values and institutions abroad.