What happened on August 20 ?

636 - Battle of Yarmuk: Arab forces led by Khalid bin Walid take control of Syria and Palestine away from the Byzantine Empire, marking the first great wave of Muslim conquests and the rapid advance of Islam outside Arabia.

917 - Battle of Anchialus: Tsar Simeon I of Bulgaria invades Thrace and drives the Byzantines out.

1391 - Konrad IV von Wallenrode becomes the 24th Grand Master of the Teutonic Order.

1794 - Battle of Fallen Timbers - American troops force a confederacy of Shawnee, Mingo, Delaware, Wyandot, Miami, Ottawa, Chippewa, and Potawatomi warriors into a disorganized retreat.

1804 - Lewis and Clark Expedition: The "Corps of Discovery", exploring the Louisiana Purchase, suffers its only death when Sergeant Charles Floyd dies, apparently from acute appendicitis.

1833 - Nat Turner leads his revolt against the Southern plantation owners of Southampton County, Virginia

1882 - Piotr Ilyitch Tchaikovsky's 1812 Overture debuts in Moscow.

1888 - Mutineers imprison Emin Pasha at Dufile.

1900 - Japan's primary school law is amended to provide for four years of mandatory schooling.

1914 - World War I: German forces occupy Brussels.

1920 - The first commercial radio station, 8MK (WWJ), begins operations in Detroit, Michigan.

1926 - Japan's public broadcasting company, Nippon H?s? Ky?kai (NHK) is established.

1938 - Lou Gehrig hits his 23rd career grand slam--a record that still stands.

1940 - Exiled Russian revolutionary Leon Trotsky is fatally wounded in Mexico City by an assassin's ice axe. He will die the next day.

1944 - The Battle of Romania begins with a major Soviet offensive.

1955 - In Morocco, a force of Berbers from the Atlas Mountains region of Algeria, raid two rural settlements and kill 77 French nationals.

1960 - Senegal breaks from the Mali federation, declaring independence.

1968 - 200,000 Warsaw Pact troops and 5,000 tanks invade Czechoslovakia to end the "Prague Spring" of political liberalization.

1975 - Viking program: NASA launches the Viking 1 planetary probe toward Mars.

1977 - Voyager program: The United States launches the Voyager 2 spacecraft.

1982 - Lebanese Civil War: A multinational force lands in Beirut to oversee the PLO withdrawal from Lebanon.

1986 - In Edmond, Oklahoma, US Postal employee Patrick Henry Sherrill guns down 14 of his co-workers and then commits suicide.

1988 - Peru becomes a member of the Berne Convention copyright treaty.

1989 - In Beverly Hills, California, Lyle and Erik Menendez shoot and kill their wealthy parents.

1991 - Collapse of the Soviet Union: More than 100,000 people rally outside the Soviet Union's parliament building protesting the coup aiming to depose President Mikhail Gorbachev. Estonia reclaimed its independence and seceded from the Soviet Union. Estonia had been occupied by the Soviets for more than 50 years.

1993 - After rounds of secret negotiations in Norway, the Oslo Peace Accords were signed, followed by a public ceremony in Washington, D.C. the next month.

1994 - Circus elephant trainer Allen Campbell is crushed to death in Honolulu, Hawaii, by the performing elephant "Tyke".

1997 - Souhane massacre in Algeria; over 60 people killed, 15 kidnapped.

1998 - The Supreme Court of Canada states Quebec cannot legally secede from Canada without the federal government's approval.

1998 - U.S. embassy bombings: The United States military launches cruise missile attacks against alleged al-Qaida camps in Afghanistan and a suspected chemical plant in Sudan in retaliation for the August 7 bombings of American embassies in Kenya and Tanzania. The al-Shifa pharmaceutical factory in Khartoum is destroyed in the attack.