Background: 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.