on behalf of Poland if hostilities broke out between the two countries. August 2 The Einstein-Szilárd letter is sent to President Roosevelt. Written by Leó Szilárd and signed by Albert Einstein, it warned of the danger that Germany might develop atomic bombs. This letter prompted action by Roosevelt and eventually resulted in the Manhattan Project. August 23 The Molotov–Ribbentrop Pact is signed between Nazi Germany and the Soviet Union, with secret provisions for the division of Eastern Europe – joint occupation of Poland and Soviet occupation of Estonia, Latvia and Lithuania, Finland and Bessarabia. This protocol removes the threat of Soviet intervention during the German invasion of Poland. August 25 In response to a message from Mussolini that Italy will not honor the Pact of Steel if Germany attacks Poland, Hitler delays the launch of the invasion by five days to provide more time to secure British and French neutrality. August 30 German ultimatum to Poland concerning the Polish Corridor and the Free City of Danzig. September 1 Without response to its ultimatum, Germany invades Poland, start of World War II (the Soviet Union invades Poland on September 17). See also International relations (1919–1939) Causes of World War II Timeline of World War I Timeline of World War II Events preceding World War II in Europe Events preceding World War II in Asia Notes and references Further reading Thorne, Christopher G. The Approach of War, 1938-1939 (1969) chronological table 1938-1939 pp 205-210 External links French Yellow Book Nazi-Soviet relations 1939-1941 Nazi-Soviet relations 1939-1941 (complete) British War Bluebook 20th-century timelines Events preceding World War II History of international relations Interwar period Modern history timelines de:Chronologie Zweiter Weltkrieg#Vorgeschichte