Governments not only interact with the people they rule but also with other
governments—to trade, to share ideas, to work together to solve global problems, and
to resolve disputes. Political scientists have been analyzing international
relations— relations between states—for centuries, but never more so than during the
twentieth century, as scholars tried to explain the reasons for and explore the
aftermath of World Wars I and II and the Cold War that followed.
Although numerous international agreements and institutions exist to
facilitate smooth relations among the nearly 200 countries in the world,
international politics can still be extremely violent. Even though people have
fought one another for millennia, political scientists still do not know exactly
what causes people and states to go to war, start revolutions, or commit acts of
terrorism. Identifying both immediate and long-term causes and consequences of
political violence, as well as thinking about the impact of this violence on the
international system, has become an important part of political science.
