Online archival resources

United States

Foreign Relations of the United States series. Check here and here for online versions.
Presidential Library webpages. For example, here. Each president has their own. Clinton’s is surprisingly good for 1990s-era material.
Specific U.S. government agency websites. Most important is the CIA’s CREST system. See also here. Other agencies, such as Department of Defense and National Security Agency, have portals as well. NRO’s is here. In general, search Google for the department/agency name and “FOIA” or “electronic reading room.”
Blogs. National Security Archive. Matthew Aid’s blog. Restricted Data blog. The Reagan Files.
Private for-fee collections/databases. Our library system has access to only some of these (check here). If not, you may be able to access them through other unversities or colleges, including Chicago-area locations like Northwestern. Digital National Security Archive. Declassified Document Reference System (now called Gale Declassified Documents Online). Archives Unbound. Proquest History Vault. BrillOnline Primary Sources. Hathi Trust Digital Library.

For non-U.S. archives, start with this guide: State Department’s World Wide Diplomatic Archives Index. Browse to country of interest
Guide to archives in the “Third World”
Wilson Center’s Digital Archive collection covers many countries
United Nations archive
World Bank archive
NATO archive

Documents on British Foreign Policy
Documents on British Policy Overseas
National Archive website, including digitized version of many records such as Cabinet Office records (here)
Margaret Thatcher Foundation archival collection here
British Online Archives (subscription required) here