Modern medicine, atomic energy, computers, and new concepts of time, energy, and matter all have an important effect on life in the 20th century.

Keeping up with the ever-increasing pace of change became the standard of the day.

Burdened with the legacy of colonial imperialism, the Third World rushed development to catch up with its Western counterparts.

The U.S. and Soviet Union dominated Europe and confronted each other in Korea.

World War II was a war of new tactics and strategies. Civilian populations became targets as the Nazi holocaust exterminated millions of people.

Old empires crumbled during World War I to be replaced by right-wing dictatorships in Italy, Spain, and Germany.

Everyday life of the working class was transformed by leisure, prompting the birth of an elite avant-garde movement.

Public education and mass communications created a new political life and leisure time.

The great powers cooperated to quell internal revolts, yet competed to acquire colonies.

Leaders in the arts, literature, and political theory argued for social justice and national liberation.

A consumer revolution was fueled by coal, public transportation, and new city services.

Technology and mass production reduced famine and ushered in higher standards of living.

Liberty, equality, and fraternity skidded into a reign of Terror.

In France the old order collapsed under revolutionaries' attacks and the monarchy's own weakness.

A new republic, the compromise of radicals and conservatives, was founded on universal freedoms.

The British colonists created a society that tested Enlightenment ideas and resisted restrictions imposed by England.

Freedom of thought and expression opened new vistas explored by French, English, and American thinkers.

Scientists and social reformers battled for universal human rights during a peaceful and prosperous period.

Intellectual theories about the nature of man and his potential came to the fore.

Monarchs considered reforms in order to create more efficient societies, but not at the expense of their own power.

Arguments about the legitimate source of political power centered on divine right versus natural law.

Exhausted by war and civil strife, many Europeans exchanged earlier liberties and anarchies for greater peace.

Amid religious wars, a few cities learned that tolerance increased their prosperity.

For more than a century, the quarrels of Protestants and Catholics tore Europe apart.

As the cities grew, new middle-class mores had an impact on religious life.

Voiced by Martin Luther, Protestantism shattered the unity of the Catholic Church.

The discovery of America challenged Europe.

Renaissance humanists made man "the measure of all things." Europe was possessed by a new passion for knowledge.

A new urban middle class emerged, while dynastic marriages established centralized monarchies.

Two hundred years of war and plague debilitated Europe.

The great churches embodied the material and spiritual ambitions of the age.

Famine, disease, and short life expectancies were the conditions that shaped medieval beliefs.

Bishop, knight, and peasant exemplified some of the social divisions of the year 1000 A.D.

Amid invasion and civil disorder, a military aristocracy dominated the kingdoms of Europe.

Charlemagne revived hopes for a new empire in Western Europe.

Barbarian kingdoms took possession of the fragments of the Roman Empire.

Nearly a thousand years after Rome's fall, Constantinople was conquered by the forces of Islam.

From Constantinople, the Byzantine Empire carried on the traditions of Greece and Rome.

Despite the success of emperors such as Hadrian and Marcus Aurelius, Rome fell victim to barbarian invasions.

While enemies slashed at Rome's borders, civil war and economic collapse destroyed the empire from within.

The old heresy became the Roman empire's official religion under the Emperor Constantine.

Christianity spread despite contempt and persecution from Rome.

Rome's civil engineering contributed as much to the empire as did its weapons.

Through its army, Rome built an empire that shaped the West.

Hellenistic kingdoms extended Greek culture throughout the Mediterranean.

Alexander's conquests quadrupled the size of the world known to the Greeks.

Socrates, Plato, and Aristotle laid the foundation of Western intellectual thought.

Democracy and philosophy arose from Greek cities at the edge of the civilized world.

Metals revolutionized tools, as well as societies, in the empires of Assyria, Persia, and Neo-Babylonia.

Settlements in the Fertile Crescent gave rise to the great river civilizations of the Middle East.

Egyptian irrigation created one of the first great civilizations.

The origins of the human race are traced from anthropoid ancestors to the agricultural revolution.