May 1, 1960.  An American U-2 spy plane piloted by Francis Gary Powers was shot down over Central Russia. Powers was tried, convicted and sentenced to 10 years in prison, but was released in exchange for an imprisoned Soviet spy.

May 4, 1886.  The Haymarket Square Riot occurred in Chicago after 180 police officers advanced on 1,300 persons gathered in the square listening to speeches of labor activists and anarchists. An incendiary device  thrown by an unknown person caused police to open fire and led to the death of several people, including eight policemen.

April 2, 1513.  Spanish explorer Ponce De Leon sighted Florida and claimed it for Spain. His landing site is now present day St. Augustine -  the oldest city in the continental United States.

April 4, 1949. NATO (the North Atlantic Treaty Organization) was created with the signing of a treaty by twelve nations united for common military defense against the threat of expansion by Soviet Russia into Western Europe.

March 1, 1781. The Articles of Confederation were ratified by Congress. Under the Articles, Congress was the sole governing body of the new American national government, which consisted of the 13 original states. They remained in effect throughout  the Revolutionary War, until the U.S. Constitution was adopted in 1789.

March 1, 1974.  Seven former high-ranking officials of the Nixon White House  - including former chief of staff, H.R. Haldeman, top aide John Ehrichman, and former attorney general, John Mitchell - were indicted for conspiring to obstruct the investigation into the Watergate break-in.

Spanning five centuries, details the lives of sixteen women who've made significant contributions to the fields of science and medicine.