American Foreign Policy has changed significantly during America's history. Foreign affairs are handled by the State Department, which is part of the Executive Branch. As Commander in Chief, the President of the United States has significant oversight of the American Military. Within the Legislative Branch, Congress must approve treaties made by American Presidents (House of Representatives), and declare War (Senate).
A key resource for historical study of American foreign policy is FRUS (Foreign Relations of the United States), an official documentary historical record of major U.S. foreign policy decisions and significant diplomatic activity. Records exist from 1870 (Lincoln), and are now being prepared for the George H. W. Bush Administration (1989-1992).