Complex sentence: They practiced Judaism secretly for over a century before openly returning to their faith; at the turn of the 21st century around 10,000 lived in Israel another 4,000 in New York City, and 1,000 elsewhere.
Split into simpler sentences: They practiced Judaism secretly for over a century before openly returning to their faith. At the turn of the 21st century, around 10,000 lived in Israel, another 4,000 in New York City, and 1,000 elsewhere.