Communism.
Lenin forced Jews out of Russia and made Russian Orthodox churches military targets. Atheism (or absence of religious organizations) was made the law of the land, at significant loss of life before the fall of communism in the 80s.
In 1987, three world-changing events took place:
1--Gorbachev made a single statement about the fact that he won't oppose some social issue that existed in Poland, and as a result, all the anti-communist political activist groups came out of hiding and overthrew the communist party in fair elections. Seeing that, almost a dozen other Eastern Bloc countries were inspired and did the same thing in their own countries, and Gorbachev found himself losing 1/4 of the Soviet Union and really unpopular in his own country.
2--Jews began flooding out of the Soviet Union to escape religious oppression. Israel's population skyrocketed, and for the first time since their founding, there were so many immigrants that they had to change their "open door policy" to Jews from around the world moving to Israel.
3--Russian Orthodox churches began popping up all over the country almost over night, finally freed from their religious oppression and no longer having to meet in secret.
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"Those who don't learn from history are forced into the ignoble ranks of the idiots who came before them."