"The twentieth century was studded with extraordinary achievements in medicine, science, technology, and space. Though for all its positive attributes, this century was the most violent in history, killing an estimated 30 million people in cold-blooded genocides, and, in wars, an estimated 187 million people. There was not a single year in the hundred-year span when there were no significant wars. In each chapter I have chosen several men and women, many not well-known, on whom I focus a bit more than other historical actors. In most cases, they reflect the spirit of their times, though generally their approaches and contributions are distinctively nuanced. Existing in a climate primed for war and violence, they, like everyone else, had to decide where their source of political identity lay and, when a decision was necessary, where their political allegiance would fall. To their own lives as individuals in a specific locality? Or to a particular nation? Or to the larger global community? Given that this allegiance factor has been much discussed during the last half of the century up through today, to what geographical level do we see world citizens committing their allegiance? That answer will be a key determinant of the future of the world. This chronological narrative also traces other crucial twentieth century developments: women and their professional and social roles, goals, successes, and setbacks; the powerful forces of race and ethnicity; the role of identity; environmental issues, including atomic energy and the sustainability of natural resources; the causes and changing nature of wars around the world; and the historical roles of contingency and memory"--