In terms of sheer numbers, which religion is responsible for the most deaths? How does that compare to the number of deaths for the sake of atheism? What about the number of atheists killed for their beliefs vs. the number of religious martyrs?
The main difficulty is answering this series of questions is that the only way to produce neat numbers would be to ignore many crucial historical facts and interpretive problems. So it's important to think about what sorts of analysis you need to do before you can even investigate that claim.
1. Statistics, especially from many premodern cultures, can be wildly inaccurate. We don't even have accurate estimates of the deaths even in the relatively well documented Peloponnesian wars, much less smaller conflicts.
2. In many ancient wars, epidemics and starvation killed many more people than were killed by actual enemy soldiers. Do people who died of disease during a religious war count as dying due to religion?
3. How can you tell what the actual motivations were in wars? Were the Crusades motivated primarily by religious beliefs or by a pragmatic desire to conquer and loot rich territories?
4. In cases where groups differ in language and ethnicity as well as religion, how can you separate discrimination based on religion from that based on other factors?
5. The world population has expanded greatly in the past few decades. How do you compare, for example, the act of completely exterminating a city of 10,000 people with that of killing 200,000 out of a city of 10 million? Is the issue sheer numbers or percentages?
6. Every war has two sides. When Christians and Muslims were fighting the Crusades, for example, should the deaths be attributed to one religion or divided equally among both sides? Islamic and Christian history books tell very different stories about these wars.
Some of the major historical episodes you might find of interest:
Hitler: Not only did Hitler kill somewhere between 5 and 6 million Jews, but there were almost 20 million Russian (atheist) casualties in World War II. Thus Hitler, an atheist, was responsible for the deaths of both Jews and atheists (as well as gypsies and homosexuals). Rather than describe his rationale as atheistic, though, we should probably just say that he was paranoid and delusional.
Stalin: Stalin, an atheist, may have been responsible for the deaths of many millions of people, but it's is difficult to estimate accurate numbers, because as well as the people he sent to forced labor camps, often for ideological reasons, many starved due to his economic mismanagement.
Iran-Iraq War of 1980-1988: Although these wars were religious in the sense of pitting Shia against Sunni Muslims, the two groups also have ethnic differences (Iraqis are Arabs and Iranians, the descendants of ancient Persia, speak an Indo-European language). Historians estimate over 500,000 deaths on each side.
Crusades: The total death toll is somewhat hard to estimate accurately, but was probably at least 2 million. It is important to note that the Roman Catholic crusaders sacked the Eastern Orthodox Christian city of Constantinople (modern Istanbul) as well as attacking Muslims and some Jews.
Gheghis Khan and the Mongol Conquests: Although Genghis Khan himself was a shamanist, he established religious freedom throughout his empire. Thus the 30 million odd deaths of the Mongol conquests probably could not be attributed to religious motives, even if the conquered peoples were mainly of religions different from his.
It would be possible to add several dozen more examples of conflicts with death tolls of over a million. Other historic episodes, such as the Salem witch trials, St. Bartholomew's Day massacre, the Cambodian genocide, and the Spanish Inquisition were equally horrific in their own ways, despite smaller death tolls. Perhaps all we can really conclude from the evidence is that the motives people have for killing each other are varied, and that no one group or ideology has a monopoly on evil.
It all depends on period and place. Certainly in several Islamic countries over the past few years Christians have tended to be victims of religious persecutions. The attacks on the Yazidis have also been in the news. In India, there have been several attacks by Hindus on Muslims, and in Sri Lanka Buddhist persecution of Hindus.
In recent decades, the many Christian countries in the global north have tended to be liberal democracies, and thus less likely to engage in religious persecution (though from the Islamic point of view, the wars in Iraq and Afghanistan were anti-Muslim). In Africa, some Christians have been persecuting homosexuals, but others, such as the South African Anglican church under the leadership of Archbishop Tutu have been models of tolerance.
Just as extremists such as the Islamic State do not represent all Muslims, so Uganda is not the same as Canada or Denmark where several Christian churches perform gay marriages.
Thank you professor, just one more, pew, and other research sites have been throwing around a number recently that 80%,or 4 out of 5 times there is an instance of religious persecution, it is against Christians... I find this hard to believe, because my perception of Christians runs more toward the oppressors that the oppressed , your thoughts?