When did your religion almost become extinct or became extinct in history before its revival?

Norse Paganism and Christianity fought against each other for influence over Scandinavia from the 8th Century all the way until the 12th Century, when the Kingdom of Sweden, who were the last Norse Pagans, became Christian and destroyed the Uppsala Temple in the early 1080s. Despite this, Norse Paganism survived as non-worshipped folklore, and Benjamin Thorpe mentioned that "the traditions and tales of Odin still live within the mouths of the Swedes" in the 19th Century. Norse Paganism came back in the 20th Century and still exists today.