Modern Era
Soviet Invasion of Poland (1939): The Nazi-Soviet Partition
The Soviet Union occupied and annexed about half of Poland's territory, sealing the country's partition with Nazi Germany.
Region
Europe
Modern Era
Battle of Westerplatte (1939): Poland's Seven-Day Defence
The Polish garrison surrendered on 7 September after a week of resistance, becoming a lasting symbol of Polish defiance in 1939.
Modern Era
Operation Pied Piper (1939): Evacuating Britain's Children
About 1.5 million people were evacuated in the first days of the war, though most had returned home by early 1940 when the expected bombing did not come.
Modern Era
Bletchley Park and Enigma: Breaking Germany's Secret Codes
British codebreakers read large volumes of German military communications, producing the Ultra intelligence that shaped Allied operations throughout the war.
Modern Era
Battle of the Atlantic (1939–1945): U-Boats, Convoys and Codes
The Allies defeated the U-boat campaign, keeping Britain supplied and making possible the build-up for the invasion of Europe.
Modern Era
Winter War (1939–1940): Finland's Stand Against the Soviets
Finland kept its independence but ceded about a tenth of its territory, including Viipuri and the Karelian Isthmus, under the Moscow Peace Treaty.
Modern Era
Invasion of Poland (1939): How World War II Began in Europe
Poland was defeated and partitioned between Germany and the Soviet Union, and Britain and France declared war on Germany, beginning the Second World War in Europe.
Modern Era
Coventry Blitz (1940): The Night Coventry Cathedral Burned
About 568 people were killed, thousands of homes and St Michael's Cathedral were destroyed, and Coventry became a symbol of destruction and later of reconciliation.
Modern Era
British Home Guard (1940–1944): Dad's Army and Home Defence
The Home Guard grew to about 1.7 million men, freed regular troops for service abroad and was stood down in December 1944 once the invasion threat had passed.
Modern Era
Operation Sea Lion (1940): Hitler's Planned Invasion of Britain
The invasion was never launched; Hitler postponed it indefinitely in September 1940 after the Luftwaffe failed to win control of the air.
Modern Era
Attack on Mers-el-Kébir (1940): Britain Strikes the French Fleet
The battleship Bretagne was sunk and other ships damaged, with about 1,300 French sailors killed; Anglo-French relations broke down.
Modern Era
Bombing of Rotterdam (1940): The Raid That Forced Dutch Surrender
The historic centre of Rotterdam was destroyed by bombing and fire, and the Netherlands capitulated the same evening.