Many works of Western historians were forbidden or censored, and many areas of history were also forbidden for research because, officially, they had never happened. For this reason, Soviet historiography remained mostly outside the international historiography of the period. Translations of foreign historiography were produced (if at all) in a truncated form, accompanied by extensive censorship and "corrective" footnotes. For example, in the Russian 1976 translation of Basil Liddell Hart's "History of the Second World War" pre-war purges of Red Army officers, the secret protocol to the Molotov–Ribbentrop Pact, many details of the Winter War, the occupation of the Baltic states, the Soviet occupation of Bessarabia and Northern Bukovina, Allied assistance to the Soviet Union during the war, many other Western Allies' efforts, the Soviet leadership's mistakes and failures, criticism of the Soviet Union and other content were censored out.