I went looking for similar data and found some surprising facts. The greatest act of genocide in history in sheer nubers may have been carried out by Belgium in it’s ruthless exploitation of the Congo. Source - Wikipedia - 8 to 10 million deaths.
Hitler of course was around 6 million, although I think it was closer to 12 million deaths, if one counts Slavic victims.
Atlantic slave trade mostly destined for the Americas, including Protestant USA - 5 to 10 million deaths.
European colonisation of the Americas, including Protestant USA - at least 2 million natives killed or died for various reasons.
French Wars of Religion - outgrowth of the Reformation - 2 to 4 million people killed or died as a result of war.
Reformation in Germany - Quoted from Wikipedia - From 1618 to 1648 the Thirty Years’ War ravaged in the Holy Roman Empire. The causes were the conflicts between Catholics and Protestants, the efforts by the various states within the Empire to increase their power and the Emperor’s attempt to achieve the religious and political unity of the Empire. The immediate occasion for the war was the uprising of the Protestant nobility of Bohemia against the emperor (Defenestration of Prague), but the conflict was widened into a European War by the intervention of King Christian IV of Denmark (1625-29), Gustavus Adolphus of Sweden (1630-48) and France under Cardinal Richelieu, the regent of the young Louis XIV (1635-48). Germany became the main theatre of war and the scene of the final conflict between France and the Habsburgs for predominance in Europe. The war resulted in large areas of Germany being laid waste, a loss of approximately a third of its population, and in a general impoverishment.
William Shirer in his “The Rise and Fall of the Third Reich” claimed the population of Germany declined from sixteen to six million and that there was a horrible torpor in the land for centuries. He commented, and he was himself a Protestant, that if he had to nominate an “evil genius” responsible for creating the state of mind which Hitler was later able to exploit, he would have to choose Martin Luther.
The Crusades - estimated death toll for all parties was around a million. Hence the Reformation was more violent in terms of deaths than the Crusades, easily.
Peasant’s War in Germany - In 1524 the Peasants’ War broke out in Swabia, Franconia and Thuringia against ruling princes and lords, following the preachings of Reformist priests. But the revolts, which were assisted by war-experienced noblemen like Götz von Berlichingen and Florian Geyer (in Franconia), and by the theologian Thomas Münzer (in Thuringia), were soon repressed by the territorial princes. It is estimated that as many as 100,000 German peasants were massacred during the revolt,[45] usually after the battles had ended.[46]
The Inquistion may have killed around 3000 people over a few hundred years. Compared to the above tallies, often carried out deliberately or inadvertently by Protestant parties as much as Catholic, it almost pales into insignificance. That doesn’t excuse the methods used by the Inquisition.
But then our atheist society of today is genially indulging in a holocaust of aborted children, with the USA alone accounting for around 800,000 each year. My own nation, Australia, has probably a similar average on a population basis. Around the world it adds up to millions. The difference is that we can’t see the unborn torn to pieces, or the scissors pushed into their brains to kill them, and they can’t protest, unlike those who think it’s a “woman’s right”.
The same nations which once went to war to put an end to Nazism are now killing an even greater number of their own people before they’ve even had a chance to live as full human beings.
We can’t keep doing that and expect God not to notice, and finally act. When He does do so, He’ll be absolutely ruthless. He’ll treat us with just the same lack of compassion we’ve demonstated to the unborn. The grim imagery in Revelation, and the dire warnings of Mary at Fatima in 1917 (which heralded the Russian Revolution almost immediately and World War II 22 years later) and Akita in Japan (1973) aren’t there for no reason.