Kammala jumla mai zuwa: A cikin shekarun 1960, Jan Křen ya zama ɗaya daga cikin masana tarihi na Czechoslovak na farko don yin rubuce-rubuce da bincike kan korar 'yan Jamus na Sudeten daga ƙasar a ƙarshen Yaƙin Duniya na II. Křen ya kasance memba ne na Jam'iyyar Kwaminis ta Czechoslovakia daga 1949 zuwa 1969, amma an fitar da shi a 1970 saboda adawarsa ga Jam'iyyar Kwaminis ta Czechoslovakia.
mamayewar Warsaw Pact. An kuma kore shi daga aikinsa na farfesa kuma aka tilasta masa ya yi aikin hannu.