 Assured by the Molotov–Ribbentrop Pact of Soviet non-interference, Germany started World War II one week later by invading Poland from the west on September 1, 1939.The Soviet Union attacked Poland from the east on September 17, and by September 28, Poland had fallen.Romanian Prime Minister Armand Călinescu, a strong supporter of Poland in its conflict with Germany, was assassinated on September 21 by elements of the Romanian far right with Nazi support.