- 1119 20 Aug Henry I defeats an invasion of his Norman lands by Louis VI, King of France, at the Battle of Brémule.
- 1944 20 Aug Two German armies are trapped and destroyed in the Falaise Gap, ending the battle for Normandy.
- 1968 20 Aug The 'Prague Spring' liberalisation in Czechoslovakia is crushed by the arrival of 200,000 Soviet troops.