Many events are not associated with a single day.
1900s – December 14, 1900: Max Planck discovers the quantum; Newton deposed, modern physics begins
1910s – Model T (cars become commonplace)
1920s – January 16, 1920: Prohibition leads to organized crime
1930s – The rise of television
1940s – August 8, 1945: Hiroshima bombed: the atomic age begins
1950s – April 25, 1953: Watson and Crick publish the structure of DNA; April 12, 1955: Salk polio vaccine released; October 4, 1957 Sputnik launched and space age begins
1960s – Liberal America assassinated and the rise of American neoconservatism: John F. Kennedy November 22, 1963, Malcolm X February 21, 1965, Martin Luther King, Jr. April 4, 1968, Robert F. Kennedy on June 6, 1968. July 20, 1969 Armstrong on the moon.
1970s – The computer age: The world's first general microprocessor — the Intel 4004, came out in November 1971.
1980s – Rise of AIDS and (Jan 20, 1981) Reaganism and rise of lawless (Iran Contra), deregulated, corporatocratic government in the west.
1990s - August 6, 1991; the new World Wide Web project (rise of the Internet and information age); Xmas 1991: fall of Soviets/eastern bloc and end of Cold War.
2000s - December 11, 2000. US Supreme Court appoints Bush president.