Molotov–Ribbentrop Pact was signed under which the Soviet Union and Nazi Germany each pledged to remain neutral in the event that either nation were attacked by a third party.
23 January — "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 airfields to launch a strategic bombing offensive against Britain. The "Dutch War Scare" leads to a major change in British policies towards Europe.
27 January — 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.
30 January — 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".
6 February — 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".
3 September – British linerSS Athenia becomes the first civilian casualty of the war when she is torpedoed and sunk by U-30 in the eastern Atlantic. Of the 1,418 aboard, 98 passengers and 19 crew are killed.
28 September — Warsaw surrenders to Germany; Modlin surrenders a day later; the last Polish large operational unit surrenders near Kock 8 days later.
October - The Action T4 programme begins, meaning that the state will now euthanise people deemed "unworthy" of life due to physical disabilities or mental illness, and keeping them alive would not be seen as good use of taxpayers money by the state or its supporters.