People seek, or claim to possess, a variety of rights: constitutional, civil, political, economic and cultural. Human rights, which many people believe are guaranteed, are arguably the best known and the least understood. The notion of human rights began to take shape after the Holocaust, so it is not surprising that Jews played an important role in their emergence. In his enlightening new book, “Rooted Cosmopolitans: Jews and Human Rights in the Twentieth Century,” James Loeffler, a historian at the University of Virginia, explores how a small group of Jewish lawyers and activists from around the world inspired the human rights movement and the creation of entities such as the United Nations that, sadly, have failed to fulfill the promises of their ideals.