The Briefing Book provides some excellent background information on national security and foreign policy, with a transparently progressive lens. In addition to offering basic guidance for understanding the military, and thoughtful, in-depth guidance on some key regions of interest, the Briefing Book also includes sections devoted to the National Security Budget; Energy & Climate Security; Immigration & Security; and Nuclear Weapons. The Truman Project provides this educational resource as a free download.
Truman Security Briefing Book