1800's, when Russia, which was in control, tried to influence the people by bringing in Russian heritage. This group also grew during World War II as other Jews fled the Nazi's.
The Mountain Jews on the other hand have a history that probably dates back over 2000 years. Many of these came from the area that is now Iran and are said to be descendants of the Jews who left Israel after the destruction of the First Temple. They survived for such a long time by settling in areas that others didn't travel, the extremely remote areas of the mountains.
When the Constitution was written in the early 1990's, religious freedom was given to all, and no state religion was declared. This freedom led to the Jewish community being somewhere between 75-100 thousand people. While the freedom still exists, many families have now emigrated to Israel, Russia or the United States because of the poor economic situation.