Many works of Western historians were forbidden or censored, many areas of history were also forbidden for research as, officially, they never happened. Translations of foreign historiography were often produced in a truncated form, accompanied with 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, Western 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.