| What is international relations?
Yes, international relations is a singular noun, referring to a discipline of the liberal arts. Traditionally, universities have integrated IR with the broader field of political science, but in many ways, IR and government are like night and day.
Compared to domestic politics, international relations is very fluid. There are no overlying governments in the international arena: instead, there are thousands of actors in the form of states, nations, IGO's, NGO's, multinational corporations, and regimes, which constantly vie for power, projecting their power struggles through war, trade, and diplomacy.
For the first several thousand years of human history, international relations consisted of epic wars and alliances between mighty and not-so-mighty kingdoms and empires. There were few formal structures in place, and in most cases, government held only tenuous power over subjects. In Western Europe, the Vatican had a degree of power above that of individual monarchs. Elsewhere, most people lived in empires, again subservient to a distant metropole of which they had only a passing knowledge.
England under Henry VIII is said to be the first example of a modern state, as the only country in the West not under some degree of papal control. For some time, however, it was pretty much the only example of a modern state. Modern international relations really began with the 1648 Treaty of Westphalia, which ended the Thirty Years' War and gave the various states of the Holy Roman Empire individual sovereignty. After Westphalia, there were many new states that had full control over themselves.
For the next handful of centuries, imperialism was the name of the game, and Europe was where its epic battles were fought. Since European states were now sovereign, battles turned from ideological ones (the Crusades to liberate Palestine) to power struggles (Napoleon Bonaparte's attempt to take over Europe). States now acted in defense of their national interests. Modern international relations had begun.
From the 18th century to the 20th century, international relations changed very little. After World War I, however, some liberal intellectuals like Woodrow Wilson sought to change the old system. They believed that the sovereignty of states was not the be-all and end-all of international relations: that there should be an element of idealism as well, to enfranchise the world's peoples and guarantee them rights and freedoms. The first attempt to accomplish this was the unsuccessful League of Nations, which collapsed in the face of World War II and was resurrected after the war as the United Nations.
The sweeping changes brought by World War II, primarily the destruction of Europe's infrastructure and the rise of weapons of mass destruction that accompanied the onset of the Cold War, completely changed international relations. After a brief honeymoon of Pax Americana, isolationism ceased to be a viable option for most states, as they found themselves needing to fall under the nuclear umbrella of one country or another. In 1946, the Cold War was officially underway, and in its wake came globalization. The need to maintain collective security brought both sides of the Iron Curtain together to the point where international trade became the norm rather than the exception.
Other relatively recent problems dogging international relations include transnational organized crime and terrorism, increased nationalism (especially in the developing world), the mass media and its increasing focus on the violation of human rights worldwide, overpopulation and famine, and the environment (pollution, deforestation, etc). Many of these problems came as a direct result of the fall of Europe's empires and the rise in international commerce.
This is why, today, international relations has become a study in its own right, rather than merely a subfield of political science. Some of its most accomplished scholars: Thucydides, Hugo Grotius, Woodrow Wilson, Henry Kissinger, Samuel Huntington, and Robert Kaplan. | 
