Like the practitioners of other beliefs including Orthodox Christians, Muslims suffered under the restriction of religious freedom by the Marxist-Leninist Zhivkov regime which instituted state atheism and suppressed religious communities. The Bulgarian communist regimes declared Islam and other religions to be "opium of the people." In 1989, 310,000 to 360,000 people fled to Turkey as a result of the communist Zhivkov regime's assimilation campaign. That program, which began in 1984, forced all Turks and other Muslims in Bulgaria to adopt Bulgarian names and renounce all Muslim customs. The motivation of the 1984 assimilation campaign was unclear; however, many experts believed that the disproportion between the birth rates of the Turks and the Bulgarians was a major factor. The event became known as "the revival process" or "the renaming." Bulgarian historian Antonina Zhelyazkova estimated that, during the period of 1990–1996, almost 400,000 more people from Bulgaria emigrated to Turkey in a second "revival process."