Afghanistan , officially Islamic Republic of Afghanistan, republic (2005 est. pop. 29,929,000), 249,999 sq mi (647,497 sq km), S central Asia. Afghanistan is bordered by Iran on the west, by Pakistan on the east and south, and by Turkmenistan, Uzbekistan, and Tajikistan on the north; a narrow strip, the Vakhan (Wakhan), extends in the northeast along Pakistan to the Xinjiang Uygur Autonomous Region of China. The capital and largest city is Kabul .

global warming the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution . The temperature of the atmosphere near the earth's surface is warmed through a natural process called the greenhouse effect.

immigration entrance of a person (an alien ) into a new country for the purpose of establishing permanent residence. Motives for immigration, like those for migration generally, are often economic, although religious or political factors may be very important. High rates of immigration are frequently accompanied by militant, and sometimes violent, calls for immigration restriction or deportation by nationalist groups. See also naturalization .

French Revolution political upheaval of world importance in France that began in 1789. Origins of the Revolution Historians disagree in evaluating the factors that brought about the Revolution. To some extent at least, it came not because France was backward, but because the country's economic and intellectual development was not matched by social and political change.

United Nations (UN), international organization established immediately after World War II. It replaced the League of Nations . In 1945, when the UN was founded, there were 51 members; 192 nations are now members of the organization (see table entitled United Nations Members ). Organization and Principles The Charter of the United Nations comprises a preamble and 19 chapters divided into 111 articles.

Federal Reserve System central banking system of the United States. Established in 1913, it began to operate in Nov., 1914. Its setup, although somewhat altered since its establishment, particularly by the Banking Act of 1935, has remained substantially the same. Structure The Federal Reserve Act created 12 regional Federal Reserve banks, supervised by a Federal Reserve Board. Each reserve bank is the central bank for its district.

food adulteration act of intentionally debasing the quality of food offered for sale either by the admixture or substitution of inferior substances or by the removal of some valuable ingredient. The Greek and Roman classics contain allusions to wine makers and dealers who colored and flavored their wine.

Tiananmen Square large public square in Beijing , China, on the southern edge of the Inner or Tatar City. The square, named for its Gate of Heavenly Peace (Tiananmen), contains the monument to the heroes of the revolution, the Great Hall of the People, the museum of history and revolution, and the Chairman Mao Zedong Memorial Hall (with Mao's embalmed body). Mao Zedong proclaimed the founding of the People's Republic in the square on Oct. 1, 1949, an anniversary still observed there.