World War II is generally considered to have started on September 1, 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. This invasion prompted the United Kingdom and France to declare war on Germany on September 3, 1939, marking the official outbreak of the war
. Before the invasion, Germany and the Soviet Union signed the Molotov- Ribbentrop Pact (a non-aggression treaty) on August 23, 1939, which secretly included plans to divide Poland between them. This pact allowed Germany to attack Poland without fear of Soviet intervention, and the Soviet Union invaded Poland from the east shortly after Germany's invasion began
. While Japan had been engaged in military aggression in Asia since 1931 and invaded China in 1937, the European conflict is conventionally marked by Germany's invasion of Poland in 1939 as the start of World War II
. In summary, Nazi Germany, led by Adolf Hitler, initiated World War II by invading Poland on September 1, 1939, with the Soviet Union also complicit through their pact with Germany
