Realism

Realism, in regard to international relations, is the approach that emphasizes the self-interest of the state within a competitive system. Don’t worry, I’m going to break this down. The realism approach regards the international community as more or less competitive, meaning each state acts in its own best interest at the expense of others. This sounds reasonable, right? The United States does what is right for the United States; Canada does what is right for Canada; Great Britain does what is right for Great Britain, and so on and so forth. The states themselves are the main actors, and there is no authority above the states to regulate their behavior. The international system is considered to be anarchic, which in this sense basically means competitive. The realism approach recognizes that state-on-state antagonism is natural and that the desire to accumulate resources is natural. Basically, in a nutshell, a foreign policy realist would tell you each state is looking out for number one.
Thomas Hobbes and Niccolò Machiavelli were leading pioneers of realist theory. While there is considerable debate over this, many historians regard the Founding Fathers’ foreign policy as rooted in realism. Many historians argue realism was the predominant American approach until World War I. George F. Kennan, a Cold War Era U.S. ambassador and leading political theorist, is widely considered a realist.
Liberalism
Okay, so we often think of liberalism as a leftist political philosophy — you know, Bill Clinton, Barack Obama, Democrats, the opposite of conservatism. Here we’re talking about a different type of liberalism. In regard to foreign affairs, liberalism is a little bit difficult to define because it is somewhat vague, but basically it is the approach that emphasizes states establishing consistent internal political philosophies that promote peace and cooperation. Whereas realism regards the international system as innately anarchic and competitive, liberalism regards long-term cooperation and harmony as attainable. Liberalism tends to emphasize issues of ethics, morality, and benevolence. Liberalism also tends to emphasize the role of international peace-keeping organizations (like the United Nations) in regulating the actions of states. This type of liberalism is highly idealistic. Sometimes it is even called idealism. It is also closely related to Wilsonianism, the foreign policy approach put forth by American President Woodrow Wilson. Wilsonianism emphasizes interventionism, global cooperation, democracy, and capitalism. Since World War I, liberalism has been a leading international relations approach. The United Nations is rooted in liberal thinking. Again, remember, we’re not talking about liberal versus conservative here in terms of political perspective; we’re talking about international relations, so the term’s meaning is a little different. Don’t get confused by that.