WHAT ALL HAPPENED AUGUST TO SEPTEMBER 1939
Find out what all happened August to September 1939

Albert Einstein and Leó Szilárd write a letter to Franklin D. Roosevelt, urging him to begin the Manhattan Project to develop a nuclear weapon. (2. August 1939)

General Władysław Sikorski becomes commander-in-chief of the Polish Government in exile. (30. September 1939)

World War II: The Battle of Barking Creek. (6. September 1939)

World War II: France, the United Kingdom, New Zealand and Australia declare war on Germany after the invasion of Poland, forming the Allies. (3. September 1939)

World War II: a Bristol Blenheim is the first British aircraft to cross the German coast following the declaration of war and German ships are bombed. (4. September 1939)

Switzerland mobilizes its forces and the Swiss Parliament elects Henri Guisan to head the Swiss Army (an event that can happen only during war or mobilization). (1. September 1939)

World War II: South Africa declares war on Germany. (6. September 1939)

Taisto Mäki becomes the first man to run the 10,000 metres in under 30 minutes, in a time of 29:52.6 (17. September 1939)

Romanian Prime Minister Armand Călinescu is assassinated by far-right legionnaires of the fascist paramilitary organization called the Iron Guard. (21. September 1939)

World War II: The Estonian military boards the Polish submarine ORP Orzeł in Tallinn, sparking a diplomatic incident that the Soviet Union will later use to justify the annexation of Estonia. (14. September 1939)

World War II: Germany and the Soviet Union sign a non-aggression treaty, the Molotov-Ribbentrop Pact. In a secret addition to the pact, the Baltic states, Finland, Romania, and Poland are divided between the two nations. (23. August 1939)

Warsaw surrenders to Nazi Germany during World War II. (28. September 1939)

World War II: The Battle of Hel begins, the longest-defended pocket of Polish Army resistance during the German invasion of Poland. (9. September 1939)

Adolf Hitler signs an order to begin the systematic euthanasia of mentally ill and disabled people. (1. September 1939)

Nazi Germany and the Soviet Union agree on a division of Poland after their invasion during World War II. (28. September 1939)

Burmese national hero U Ottama dies in prison after a hunger strike to protest Britain's colonial government. (9. September 1939)

World War II: The Battle of Kępa Oksywska concludes, with Polish losses reaching roughly 14% of all the forces engaged. (19. September 1939)

World War II: A German U-boat U 29 sinks the British aircraft carrier HMS Courageous. (17. September 1939)

World War II: Nazi Germany and Slovakia invade Poland, beginning the European phase of World War II. (1. September 1939)

World War II: The United Kingdom and France begin a naval blockade of Germany that lasts until the end of the war. This also marks the beginning of the Battle of the Atlantic. (3. September 1939)