The Wilson Center Digital Archive offers many collections of declassified historical documents. The documents contain memos and transcripts of communications between diplomats and country leaders. The collections are arranged into topics and themes. You’ll find collections of documents related to the construction of the Berlin Wall, the origins of the Cold War, Sino-Soviet relations, and diplomatic efforts related to nuclear weapons.
Applications for Education
My first thought when looking at these collections of documents was to have students use these documents to fill-in the gaps in their history textbooks.
You could also give students some of the communications without the names of countries or diplomats showing. Then ask them to use their knowledge of the situation to determine which country or diplomat would have sent that communication.