After the war he was a member of Yugoslav delegation on 1946 Paris peace conference and on several sessions of United Nations General Assembly (1945-1952). In 1952 he became a member of the Party's Central Committee and was excluded from it following the fall of Milovan Đilas. From then on, he devoted himself to writing history and teaching (he taught at Belgrade University and at universities in United Kingdom and United States).
One of his most famous books is The Yugoslav Auschwitz and the Vatican: The Croatian Massacre of the Serbs During World War II which was translated in several languages. Another book, The Road to Sarajevo, discusses the origins of World War I.
He wrote two important accounts of Partisan history: Diary and Tito, both of which have been published in English.
He was Chairman and President of Sessions at the 1966 Russell Tribunal.