20 July plot
On 20 July 1944, Claus von Stauffenberg and other conspirators attempted to assassinate Adolf Hitler, Führer of Nazi Germany, inside his Wolf’s Lair field headquarters near Rastenburg, East Prussia. The name Operation Valkyrie—originally referring to part of the conspiracy—has become associated with the entire event.
The apparent aim of the assassination attempt was to wrest political control of Germany and its armed forces from the Nazi Party (including the SS) and to make peace with the Western Allies as soon as possible. The details of the conspirators’ peace initiatives remain unknown, but they would have included unrealistic demands for the confirmation of Germany’s extensive annexations of European territory.
The plot was the culmination of efforts by several groups in the German resistance to overthrow the Nazi German government. The failure of the assassination attempt and the intended military coup d’état that was to follow led the Gestapo to arrest more than 7,000 people, of whom they executed 4,980. (Source)