1 September 1939, Nazi Germany invaded Poland " The Second World War began in Europe

https://www.history.com/this-day-in-history/germany-invades-poland

snip-"On September 1, 1939, German forces under the control of Adolf Hitler bombard Poland on land and from the air. World War II had begun.

Germany invaded Poland to regain lost territory and ultimately rule their neighbor to the east. The German invasion of Poland was a primer on how Hitler intended to wage war–what would become the “blitzkrieg” strategy.

Germany's blitzkrieg approach was characterized by extensive bombing early on to destroy the enemy’s air capacity, railroads, communication lines and munitions dumps, followed by a massive land invasion with overwhelming numbers of troops, tanks and artillery. After the German forces had plowed their way through, devastating a swath of territory, infantry moved in, picking off any remaining resistance.

Once Hitler had a base of operations within the target country, he immediately began setting up “security” forces to annihilate all enemies of his Nazi ideology, whether racial, religious or political. Concentration camps for slave laborers and the extermination of civilians went hand-in-hand with German rule of a conquered nation. For example, within one day of the German invasion of Poland, Hitler was already setting up SS “Death’s Head” regiments to terrorize the populace."


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from the wiki article on the World War II casualties

source- https://en.m.wikipedia.org/wiki/World_War_II_casualties#:~:text=Civilian%20deaths%20totaled%2050%E2%80%9355,5%20million%20prisoners%20of%20war.

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World War II was the deadliest military conflict in history. An estimated total of 70–85 million people perished, or about 3% of the estimated global population of 2.3 billion in 1940.[1] Deaths directly caused by the war (including military and civilian fatalities) are estimated at 50–56 million, with an additional estimated 19–28 million deaths from war-related disease and famine. Civilian deaths totaled 50–55 million. Military deaths from all causes totaled 21–25 million, including deaths in captivity of about 5 million prisoners of war. More than half of the total number of casualties are accounted for by the dead of the Republic of China and of the Soviet Union. "

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