ry response, and instability in the Palestinian
Authority are undermining progress toward a permanent settlement.

Western Sahara:
Morocco virtually annexed the northern two-thirds of
Western Sahara (formerly Spanish Sahara) in 1976, and the rest of
the territory in 1979, following Mauritania's withdrawal. A
guerrilla war with the Polisario Front contesting Rabat's
sovereignty ended in a 1991 cease-fire; a referendum on final status
has been repeatedly postponed and is not expected to occur until at
least 2002.

World:
Globally, the 20th century was marked by: (a) two devastating
world wars; (b) the Great Depression of the 1930s; (c) the end of
vast colonial empires; (d) rapid advances in science and technology,
from the first airplane flight at Kitty Hawk, North Carolina (US) to
the landing on the moon; (e) the Cold War between the Western
alliance and the Warsaw Pact nations; (f) a sharp rise in living
standards in North America, Europe, and Japan; (g) increased
concerns about the environment, including loss of forests, shortages
of energy and water, the drop in biological diversity, and air
pollution; (h) the onset of the AIDS epidemic; and (i) the ultimate
emergence of the US as the only world superpower. The planet's
population continues to explode: from 1 billion in 1820, to 2
billion in 1930, 3 billion in 1960, 4 billion in 1974, 5 billion in
1988, and 6 billion in 2000. For the 21st century, the continued
exponential growth in science and technology raises both hopes
(e.g., advances in medicine) and fears (e.g., development of even
more lethal weapons of war).

Yemen:
North Yemen became independent of the Ottoman Empire in 1918.
The British, who had set up a protectorate area around the southern
port of Aden in the 19th century, withdrew in 1967 from what became
South Yemen. Three years later, the southern government adopted a
Marxist orientation. The massive exodus of hundreds of thousands of
Yemenis from the south to the north contributed to two decades of
hostility between the states. The two countries were formally
unified as the Republic of Yemen in 1990. A southern secessionist
movement in 1994 was quickly subdued. In 2000, Saudi Arabia and
Yemen agreed to a delimitation of their border.

Yugoslavia:
The Kingdom of Serbs, Croats, and Slovenes was formed in
1918; its name was changed to Yugoslavia in 1929. Occupation by Nazi