If you were to ask five people to name an area which international relations affects the most, you would likely receive five different answers. International diplomacy is a highly interconnected, interdisciplinary field. It involves expertise from areas like political science, macroeconomics, history, global ethics, globalization and geopolitics.
For this reason, international diplomacy also transcends governmental agencies. In the U.S., the State Department is responsible for diplomatic matters. However, agencies that handle economic, security, law enforcement and other issues may all be involved in international affairs and are often present in U.S. Embassies abroad.