September 1939
September 1st: Citing Polish incursions into Germany, the German Army pours over the Polish border in a massive invasion! Rumanian forces invade Poland on their own just hours later.
September 2nd: Russian and Turkey announce an exchange of diplomatic visits.
September 3rd: France and Britain declare war on Germany and Rumania.
September 5th: While German troops enter Danzig, the Polish Navy makes a break for open sea in the small hours of the morning. As a Kriegsmarine taskforce attempts to intercept, a running battle ensues. In the end, 2 Polish ships escape to the North Sea, leaving the Germans slighty stung.
September 6th: The Germans cut off any Polish escape to Hungary.
September 7th: As another Kriegsmarine Task Force attempts to run the Channel, they are met by a large Royal Navy contingent. After suffering major damage, the Scharnhorst tries to lead the Germans back to the safety of the Baltic. Not content to let the Germans slip away unmolested, the British keep up pursuit. In the end, the Brits lose one light cruiser and most of the Ark Royal's planes for 4 German destroyers.
September 8th: More bad news for the German Navy. England claims 3 U-boats sunk in a single day.
September 9th: After being stalled at the border for 8 days, the Rumanians clear out the last of the Polish permanent defenses, and head towards Stanislow.
September 10th: German troops force their way into the heart of Warsaw.
September 13th: Poland surrenders to the German and Romanian invaders!
September 14th: Rumanian troops move to occupy Stanislow peacefully, sparing the city any damage.
September 17th: Russian troops cross into Poland and take control of a little less than half the country peacefully. German troops withdraw to a mutual new border.
September 29th: British sources claim 20 German U-boats for the loss of 2 destroyers and 10% of their monthly shipping. Germany counters with claims of 5 British destroyers and 15% of shipping for much less than 20 U-boats.
Thanks to Matt Frederiksen (GM) for this.