https://en.wikipedia.org/wiki/Eastern_Front_(World_War_I)Russia:
6,800,000-9,000,000+
Civilian deaths:
2,000,000+
Russian Empire:
410,000 civilians died due to military action
730,000 civilians died of war-related causes[14]
https://en.wikipedia.org/wiki/Destruction_of_KaliszThe German army invaded Kalisz on 2 August 1914. The town was burnt down; only churches and public offices survived. A significant number of citizens were shot. Prior to the war, Kalisz had 65,000 inhabitants. Afterwards, it was left with 5,000 inhabitants.
https://en.wikipedia.org/wiki/Serbian_campaign450,000[1] to 842,000[2] Serbian civilians died of war-related causes from 1914 to 1918
the Kingdom of Serbia lost more than 1,200,000 inhabitants during the war (including both military and civilian losses), which represented more than 29% of its overall population and 60% of its male population.[11][12]
https://en.wikipedia.org/wiki/Eastern_Front_(World_War_II)>around 30 million occurred on the Eastern Front, including 9 million children.[9][l]https://en.wikipedia.org/wiki/Generalplan_OstDeaths
11 million Slavs[5]
3-3.4 million Polish Jews[6]
https://en.wikipedia.org/wiki/Usta%C5%A1ewhile estimates of Serb victims range from 200,000 to 500,000,[125] with historians generally listing between 300,000 and 350,000 deaths.[126][127][128][129]
The history textbooks in the Socialist Federal Republic of Yugoslavia cited 700,000 as the total number of victims at Jasenovac.
https://en.wikipedia.org/wiki/Polish_Operation_of_the_NKVDDeaths
c. 111,091
Victims
22% of the Polish population of the Soviet Union was "sentenced" by the operation (140,000 people)[3]
https://en.wikipedia.org/wiki/Soviet_repressions_of_Polish_citizens_(1939%E2%80%931946)500,000 Polish nationals imprisoned before June 1941 (90% male)[1]
22,000 Polish military personnel and officials killed in the Katyn massacre alone[2]
320,000 Poles deported to Siberia in 1939-1941[3]
possibly 100,000 women raped during the Soviet counter-offensive[4]
up to 100,000[5] or at least 150,000 killed by the Soviets[6][a]
https://en.wikipedia.org/wiki/Warsaw_Uprising80-90% of Warsaw destroyed
150,000[13]-200,000 civilians killed[14][15]
700,000 expelled from the city[8]
Polish resistance:
15,200 killed and missing[8]
https://en.wikipedia.org/wiki/Invasion_of_PolandTotal: ~874,700[Note 4]
66,000 killed
~675,000 captured
https://en.wikipedia.org/wiki/The_HolocaustDeaths
Around 6 million Jews[a]
90% of all Jews in Poland
Of the six million victims, the vast majority of those killed were from Eastern Europe, and with half from Poland, and 2.6 million within the 1941 Soviet borders.[401][402][400]
https://en.wikipedia.org/wiki/Massacres_of_Poles_in_Volhynia_and_Eastern_GaliciaDeaths
Several estimates:
50,000-100,000[1]
60,000-100,000[2]
100,000[3]
https://en.wikipedia.org/wiki/War_crimes_of_the_WehrmachtOther sources estimate that rapes of Soviet women by the Wehrmacht range up to 10,000,000 incidents, with between 750,000 and 1,000,000 children being born as a result.[132][133][134]
https://en.wikipedia.org/wiki/HolodomorAround 3.5 to 5 million in Ukraine; see death toll
Yushchenko stated in a speech to the United States Congress that the Holodomor "took away 20 million lives of Ukrainians,".[147][148] Former Canadian Prime Minister Stephen Harper issued a public statement giving the death toll at about 10 million.[149][150][151]
at the National University of Kyiv Taras Shevchenko, it was claimed that during the Holodomor 7 million Ukrainians were killed, and in total, 10 million people died of starvation across the USSR.[153]
https://en.wikipedia.org/wiki/Gulag18,000,000 people passed through the Gulag's camps[1][2][3]
53 Gulag camp directorates (colloquially referred to as simply "camps") and 423 labor colonies in the Soviet Union as of March 1940[4]
The tentative consensus in contemporary Soviet historiography is that roughly 1,600,000[b] died due to detention in the camps.[1][2][3]
Poland suffered the highest percentage of total population loss of any sovereign nation during World War II, with approximately 17% to 20% of its pre-war population killed. Poland suffered the highest percentage of total population loss of any sovereign nation during World War II, with approximately 17% to 20% of its pre-war population killed.