1400s: The Hundred Years' War, and increases in royal power and economic development, lead to the growth of national feeling and modern nation-states.

1923: World War I, which itself resulted from nationalist clashes, gives rise to a number of new nation-states, encouraging national rivalries.

Today: With the end of the cold war, which had suppressed many nationalist rivalries, old and new conflicts between nations and ethnic groups have come to the fore.

1400s: The Catholic Church is the dominant religious and political force in the Western World.

1923: The Catholic Church retains its dominant religious role in some parts of the Western World, including France and southern Europe, but elsewhere (England, the United States) it has no such dominant status.

Today: The Catholic Church, like other churches, has tried to modernize itself to broaden its appeal in an increasingly secular age.

1400s: In the traditional medieval...