By any of the customary measures we deploy to demarcate historical epochs, the twentieth century does not appear to be a very coherent unit. The beginnings and ends of what we choose to call centuries are almost invariably years of little significance. But there is little agreement over when the twentieth century c.e. arrived, and there were several points both before the year 2000 (the collapse of the Soviet Union, the reunification of Germany, the surge of globalization from the mid-1990s) and afterward (9/11, or the global recession of 2008) when one could quite plausibly argue that a new era...

Migration is a basic feature of the human species. Along with mutation and natural selection, it is one of the three basic mechanisms of human evolution. The movement of primates in central Africa gave birth to the first hominids some 5 million years ago. Movement made possible the appearance of every hominid species since then, including our own some 150,000 years ago, and the spread of Homo sapiens from our African cradle to every major area of the planet since 50,000 b.p.. These migratory currents have connected all the continents since 1500 c.e., helping create the political, social, and ethnic...

In 2006, for the first time, more than half of the world’s population lived in cities. In 1900, about one person in six lived in a city, a total of about 260 million people. By 2000, 47 percent were urban—about 3 billion people. According to United Nations estimates, the 50 percent mark was reached in 2006. Individual cities grew to enormous population size. By the end of the twentieth century, nineteen cities had become “megacities,” holding populations of 10 million or more; they expanded geographically to breathtaking proportions. The Los Angeles metropolitan region, for example, held a population of...

In 1905 an Indian journal published the fanciful story of a nation called Ladyland, where men were secluded in thezenana—the portion of the home reserved for women—while women ran the economy and political affairs. “The Sultana’s Dream” showed women using their brains to harness the sun’s energy to repel invaders, for example, and to engineer all sorts of feats to make public life easier and pleasant. The author of “The Sultana’s Dream,” Rokeya Sakhawat Hosain (1880–1932), was a self-educated Bengali woman who, as part of her patriotism, advocated the education of women and a more scientific...

The twentieth century has been marked by an intensification of rights claims and struggles in the face of egregious rights violations and abuses. This tragic coincidence has been an inescapable part of the historic development of human rights norms, strategies, and institutions. It puts in bold relief the glaring tensions between an increasingly universal moral code and the daily practices of political and military power.

From multiple perspectives, the century offered its own disturbing record of horrors—brutal colonial wars, cataclysmic eruptions of civic violence in the aftermath of the cold war, genocides, ethnic cleansings, mass rapes, and countless numbers...

This study of the First and Second World Wars represents part of the constantly ongoing efforts of historians to understand and interpret the most destructive wars in human history. The re-examination of the origins of these conflicts and of the wars themselves stems from prior revisions of the perceptions of both and suggests that historians in the long run will need to examine and understand them as an interconnected whole, though not necessarily in terms of current conceptualizations of the world wars as another Thirty Years’ War.

The major difficulty with the traditional dating of the two—the first from...

This chapter describes, and hopes to further, a budding relationship between American and world history. Since the 1940s, most conventional U.S. histories have begun with the idea that the nation has developed fundamentally apart from the rest of the world, outside the norms or constraints of global history. Challenging this exceptionalist premise, a movement to internationalize the study of American history has gained ground among scholars and teachers since the 1990s. It has been stimulated by public debates over American multiculturalism and globalization, growing American involvement in transnational movements, and concerns about the impact of American policies abroad—an issue...

Technological change played a major role in the defining events of the twentieth century, especially in war. Two world wars, the cold war, and colonial and postcolonial conflicts around the globe were all characterized by innovation in the technologies of destruction, from tanks and ballistic missiles to mass-produced automatic rifles and portable antiaircraft rockets. As the century wore on, conflicts spread well beyond the battlefield. Weapons of mass destruction rendered specious most distinctions between military fronts and protected rear areas. Mass production dropped the price of small arms into the bargain basement, while free markets made them readily available.

Across...

Throughout history, Homo sapiens [sapiens] has adapted to natural systems and used them for human purposes. But the rise of industrialization and large-scale economic organization has given human societies steadily accelerating power over the natural world. This has meant an increasingly ominous loss of the biosphere’s capacity to sustain resources for use by humans as well as other species. Global environmental change in the twentieth century accelerated some trends from the earlier industrial era, diversified others, and saw the rise of environmental management as a response to shrinking frontiers of natural resources and rising levels of pollution.

By the early...