1 The Invasion of Poland begins at 4:30
1 The United Kingdom home front is opened as the government declares general mobilization of the British army and begins evacuation plans in preparation of German air attacks.
3 The politics and diplomacy of World War II begin with frantic government responses to the attack on Poland. The United Kingdom, along with Australia and New Zealand, declare war at 11:15
3 The Second Battle of the Atlantic begins as the German navy goes into action.
4 Allied air operations in Europe begin with Royal Air Force raids on German naval targets.
7 French patrols enter Germany near Saarbrücken.
10 Canada declares war on Germany.
17 The Soviet Union invades Poland from the east, occupying the territory east of the Curzon line as well as Bialystok and Eastern Galicia.
18 Warsaw is surrounded by German troops.
25 German home front measures begin with food rationing.
27–28 Extensive bombardments of Warsaw.
28 The Polish capital, Warsaw, surrenders to the Germans.
5 The Soviet Union begins talks with Finland to adjust the border between the two countries.
6 Polish resistance in the Polish September Campaign comes to an end. Finland begins mobilizing its army. Hitler speaks before the Reichstag, declaring a desire for a conference with Britain and France to restore peace.
9 Hitler issues orders to prepare for the invasion of Belgium, France, Luxembourg, and the Netherlands.
10 The German navy suggests occupying Norway to Hitler.
14 The British battleship Royal Oak is sunk in Scapa Flow harbor by U-47.
19 Portions of Poland are formally inducted into Germany; the first Jewish ghetto is established at Lublin.
4 The Neutrality Acts are enacted in the United States, the “cash and carry” provisions for selling military supplies favor Britain and France.
8 An attempt to assassinate Hitler with a bomb while he makes a speech fails. In the Venlo Incident, two British intelligence agents are captured. Germans appoint Hans Frank governor general of Poland and begin accelerating the anti-Jewish programs there.
30 The Soviet Union attacks Finland starting the Winter War.
13 Battle of the River Plate, British naval squadron attacks the Admiral Graf Spee.
14 The USSR is expelled from the League of Nations.
17 Admiral Graf Spee scuttled in Montevideo harbor.
18 The first Canadian troops arrive in Europe.
27 The first Indian troops arrive in France.
28 Meat rationing program begins in Britain.