Reactor No. 4 of the Chernobyl nuclear power plant in Soviet Ukraine explodes, spreading radioactive material across Europe in the worst nuclear accident in history.
Mikhail Gorbachev is chosen as General Secretary of the Soviet Communist Party and goes on to launch the policies of perestroika and glasnost.
A team at the Pasteur Institute including Françoise Barré-Sinoussi and Luc Montagnier reports the virus later named HIV, the cause of AIDS.
Tim Berners-Lee submits "Information Management: A Proposal" at CERN, the origin of the World Wide Web.
East Germany opens its border and crowds cross the Berlin Wall, a symbol of the Cold War's end.
Peaceful protests in Czechoslovakia bring an end to Communist rule; Václav Havel is elected president.
Argentina seizes the Falkland Islands; Britain dispatches a task force and retakes the islands after a 74-day conflict.