This new persecution was following upon the 1975 amendments to the 1929 anti-religious legislation and the 25th party congress. The Central Committee resolution in 1979 would play a key role in this period as well. The intensification of anti-religious activities had continued since the early 1970s; between 1971 and 1975 over 30 doctoral and 400 magisterial dissertations were defended on the subjects of atheism and criticism of religion. In 1974 there was a conference in Leningrad dedicated to 'The Topical Problems of the History of Religion and Atheism in the Light of Marxist–Leninist Scholarship'.