May 15, 1911 - The United States Supreme Court declares Standard Oil to be an unreasonable monopoly under the Sherman Antitrust Act and orders it to be broken up.
May 14, 1878 - The last witchcraft trial in the he United States opens. Lucretia Brown accused Daniel Stafford of trying to harm her through "mesmeric" mental powers. It also took place in Salem.
May 11, 1997 - Deep Blue becomes the first computer to beat a chess champion in a chess match under standard tournament registrations. The match lasted from May 3 to 11 and ended with Garry Kasparov being defeated in a 6 match game.