For more see the Government Information portal at Columbia. If you are unfamiliar with how the American Government is set up (it's confusing!) please consult this fabulous set of resources from USA.gov.
Department of State: The Department of State is the primary source of foreign affairs information for the U.S. Government and is responsible for implementing the President's foreign policies.
Don't forget that the State Department has had many versions of their website that can be accessed at their web-archive.
Background Notes - U.S. Department of State: Brief profiles of most countries of the world. Includes information on government type and structure, names of major government officials, and an overview of foreign relations.
National Archives: Links and indexes to government publications in the National Archives.
Science.gov : Provide users with access to more than 200 million pages of authoritative federal science information including research and development results.
USA.gov: Official guide to government information and services