January 23 – "Dutch War Scare": Admiral Wilhelm Canaris of the Abwehr leaks misinformation to the effect that Germany plans to invade the Netherlands in February, with the aim of using Dutch air-fields to launch a strategic bombing offensive against Britain. The "Dutch War Scare" leads to a major change in British policies towards Europe.
In Paris, French Foreign Minister Georges Bonnet, in response to rumours (which are true) that he is seeking to end the French alliance system in Eastern Europe, gives a speech highlighting his government's commitment to the cordon sanitaire.
January 27 – Adolf Hitler orders Plan Z, a 5-year naval expansion programme intended to provide for a huge German fleet capable of crushing the Royal Navy by 1944. The Kriegsmarine is given the first priority on the allotment of German economic resources.
January 30 – Hitler gives a speech before the Reichstag calling for an "export battle" to increase German foreign exchange holdings. The same speech also sees Hitler's "prophecy" where he warns that if "Jewish financers" start a war against Germany, the...result will be the annihilation of the Jewish race in Europe".
British Prime Minister Neville Chamberlain states in the House of Commons that any German attack on France will be automatically considered an attack on Britain.
In a response to Georges Bonnet's speech of January 26, German Foreign Minister Joachim von Ribbentrop, referring to Bonnet's alleged statement of December 6, 1938, accepting Eastern Europe as being in Germany's exclusive sphere of influence, protests that all French security commitments in that region are "now off limits".
In Durban, South Africa the Timeless Test begins between England and South Africa, the longest game of cricket ever played. It is abandoned twelve days later when the English team has to catch the last ferry home.
March 18 – "Romanian War Scare": Virgil Tilea, the Romanian Minister in London, spreads false rumours that Romania is on the verge of a German attack.
March 19 – Hitler sends a registered letter to the government of Lithuania stating that Germany intends to annex the port of Memel.
March 20 – At an emergency meeting in London to deal with the Romanian crisis, French Foreign Minister Georges Bonnet suggests to Lord Halifax that the ideal state for saving Romania from a German attack is Poland.
American adventurer Richard Halliburton delivers a last message from a Chinese junk, before he disappears on a voyage across the Pacific Ocean. In 1945, some wreckage identified as a rudder and believed to belong to the junk, washed ashore in San Diego, California.
March 31 – Neville Chamberlain gives a speech in the House of Commons offering the British "guarantee" of the independence of Poland.
The Spanish Civil War comes to an end when the last of the Republican forces surrender.
The rumor that Hitler is dead sweeps the United States as millions of CBS radio listeners hear the Führer cut off in mid-speech during a shortwave relay of his address at the dedication of the Tirpitz in Wilhelmshaven.
At a meeting in Paris, French Foreign Minister Georges Bonnet meets with Soviet Ambassador Jakob Suritz, and suggests that a "peace front" comprising France, the Soviet Union, Great Britain, Poland and Romania would deter Germany from war.
May 6 – Carl Friedrich Goerdeler tells the British government that the German and Soviet governments are secretly beginning a rapprochement with the aim of dividing Eastern Europe between them. Goerdeler also informs the British of German economic problems which he states threaten the survival of the Nazi regime, and advises that if a firm stand is made for Poland, then Hitler will be deterred from war.
June 3 – The Soviet government offers its definition of what constitutes "aggression", upon which the projected Anglo-Soviet-French alliance will come into effect. The French Foreign Minister Georges Bonnet accepts the Soviet definition of aggression at once. The British reject the Soviet definition, especially the concept of "indirect aggression", which they feel is too loose a definition and phrased in such a manner as to imply the Soviet right of inference in the internal affairs of nations of Eastern Europe.
August 24 – As details of the Molotov–Ribbentrop Pact become public, Neville Chamberlain recalls the Parliament of the United Kingdom several weeks early. In a burst of legislation, a War Powers Act is approved; and HMG order the Royal Navy to be put on a war footing, all leaves to be cancelled, and the Naval and coast defense reserves to be called up, especially radar and anti-aircraft units. In addition, the last British and French private citizens in Germany are ordered home by their respective Governments.
The German Foreign Ministry cuts off all telegraph and telephone communication with the outside world in accordance with the plan for Fall Weiss. At approximately 1830 Central European time, Adolf Hitler postpones Fall Weiss for 5 days, after receiving a message from Benito Mussolini that he will not honor the Pact of Steel if Germany attacks Poland, and because Chamberlain's government has not fallen as a result of the German-Soviet Non-Aggression Pact. Some units already in their forward positions (the attack is scheduled for 0430 the next day) do not get the word in time and attack various targets along the border. That same day, Neville Chamberlain gives Edward Rydz-Śmigły his "ironclad guarantee" of assistance if Poland is attacked by Germany.
Opening shots of World War II and Invasion of Poland: At 4:45am Central European Time, under cover of darkness, the German WW1-era battleship Schleswig-Holstein quietly slips her moorings at her wharf in Danzig harbor, drifts into the center of the channel, and commences firing on the fortress Westerplatte, a Polish army installation at the northeastern mouth of the port of the internationalized Free City of Danzig. Five minutes previously the bombing of Wieluń in the western part of Poland had begun. Shock-troops of the German Wehrmacht begin crossing the border into Poland. Bombing of Wieluń (two air-raids) follows.
WWII: Forward elements of General Hoeppner's XVI Panzerkorps take up positions outside Warsaw. The world is stunned by the rapidity of the German advance and the Polish High Command is effectively isolated, but lack of infantry support and effective civilian resistance cause Hoeppner to halt outside the city itself.
WWII: Polish troops on the Westerplatte are forced, due to lack of food and ammunition, to surrender. The garrison of about two hundred had held out against thousands of German forces (many of them Naval officer cadets from the Schleswig-Holstein,) for seven days.
September 9 – WWII: Troops of the Polish Poznań Army under the command of General Kutrzeba open the Battle of the Bzura, the largest and best organized counter-attack mounted by the Polish forces in the campaign of 1939. For the first few days all goes well and the Germans are forced to retreat; but quick reaction by mechanized units and the Luftwaffe soon take their toll and the operation bogs down.
September 19 – WWII: The Poznan pocket collapses, and the Germans capture, according to many sources, over 150,000 men. Many elements of General Tadeusz Kutrzeba's forces work their way into Warsaw under extreme difficulty.
Reinhard Heydrich, chief of the Security Police, sends a directive, the Schnellbrief, explaining that Jews living in towns and villages in the Polish occupation zones are to be transferred to ghettos, and Jewish councils, Judenräte, will be established to carry out the German authorities’ orders.
September 24 – WWII: The Soviet Union issues an ultimatum to Estonia to allow Soviet military bases on its territory, which Estonia accepts on September 28. Similar ultimatums are issued to Latvia on October 5 and to Lithuania on October 10, who are forced to accept them as well.
November 17 – WWII: To punish protests against the Nazi occupation of the Czech homeland, the Nazis storm the University of Prague and murder nine Czech graduate students, send over 1,200 to concentration camps, and close all Czech universities, an event which will be commemorated as International Students' Day.