During the late 19^th and early 20^th centuries, many Jews from Central and Eastern Europe arrived in New York City, where they did not only find a new home, but far away from their shtetl origin, the new members of the American society also began to politically radicalize. There has been a discussion in the literature related to the field, where, how, and why the Jewish population radicalized. This study analyses two waves of radicalization: one related to the American environment that is responsible for the described process at the end of the 19^th century; one, related to the developments in Eastern Europe during the early decades of the 20^th century. For both radicalization processes this book compares the reasons, elements, and aims of those who join radical movements to show that there is a transatlantic perspective that links both processes to each other.