Realism vs. Idealism in U.S. Foreign Policy (Adrienne Mitchel)

Since the 1800s U.S. foreign policy, or the principles, practices, and goals that directs a nation in its relationships with other countries, has been greatly influenced by two differing schools of thought — realism and idealism. Realism is built on the idea that relations with other countries should be based on promoting national self-interest, and foreign policy should have practical goals which benefit America. In contrast, idealism is built on the idea that ideals and values should impact countries’ relationships, and foreign policy should advocate America's founding ideals (democracy, liberty, and rights) to improve the world for all people, not just American people. In a nutshell, realism, a more practical but more selfish vision, stresses the importance of benefiting America, and idealism, a less practical but more selfless vision, stresses the importance of benefiting the whole world. To better understand the differing viewpoints of a realist and an idealist, I will provide two examples of events that occurred in American history and explain how each school of thought felt about it.

When President Thomas Jefferson doubled the United State’s territory by buying the Louisiana territory from France, it became evident that expansionism became a new goal for U.S. foreign policy. Realists were in favor of expansionism because it made the United States more secure by ridding the nation of foreign threats on its borders, as well as giving the U.S. more growing room. Idealists were also in favor of expansionism, but for a different reason than realists — idealists believed that the United States must expand its democracy and founding ideals around the whole world, a belief called manifest destiny. 
The Mexican War, fought between the United States and Mexico over Texas, came to end with the Treaty of Guadalupe Hidalgo, in which Mexico recognized the U.S. Annexation of Texas as well as giving the U.S. a huge region of land from Texas to California. Realists were extremely satisfied with results, as the United States increased its territory by approximately one third and consequently Mexico lost about half of its territory. However, idealists believed the Mexican War was an unnecessary and unjust land grab because they believed the rights of the Mexican people were violated. 

After reading this overview of of the difference between realism and idealism, which school of thought do you think should have more influence in U.S. foreign policy?