I did some research and here's what I found. Perhaps these numbers aren't accurate?
Religious Wars in Europe:
The Crusades (1095-1291): Estimates of deaths vary widely, but it is believed that hundreds of thousands of people were killed in these series of religious wars between Christians and Muslims.
The Thirty Years' War (1618-1648): While not solely a religious war, it was deeply influenced by religious conflicts between Protestants and Catholics. Estimates suggest that up to 8 million people died, both directly and indirectly, from warfare, disease, and famine.
The Wars of Religion in France (1562-1598): These conflicts between Catholics and Huguenots (French Protestants) resulted in an estimated 3-4 million deaths.
Religious Conflicts in the Middle East:
The Ottoman-Safavid Wars (1514-1736): A series of conflicts between the Ottoman Empire and the Safavid Empire, driven by religious differences between Sunni and Shia Islam. Estimates of deaths are difficult to ascertain, but they were significant.
The Iran-Iraq War (1980-1988): While not solely a religious war, it had strong sectarian overtones between Shia and Sunni Muslims. Estimates suggest that over 1 million people were killed.
Religious Conflicts in South Asia:
The Partition of India (1947): The division of British India into India and Pakistan, largely along religious lines, resulted in an estimated 200,000 to 2 million deaths.
The Mughal-Maratha Wars (1680-1707): A series of conflicts between the Mughal Empire and the Maratha Confederacy, driven by religious and political differences. Estimates of deaths are uncertain but significant.
Religious Conflicts in Africa:
The Rwandan Genocide (1994): While not solely a religious conflict, it had strong ethnic and religious overtones. An estimated 500,000 to 1 million people were killed.
The Nigerian Civil War (1967-1970): Also known as the Biafran War, it had religious and ethnic dimensions. Estimates suggest that 1-3 million people died.
Religious Conflicts in the Americas:
The Conquest of the Americas: The Spanish conquest of the Americas in the 16th century, driven by religious zeal, resulted in the deaths of millions of indigenous people due to warfare, disease, and forced labor.
The Thirty Years' War (1618-1648): While not solely a religious war, it was deeply influenced by religious conflicts between Protestants and Catholics. Estimates suggest that up to 8 million people died, both directly and indirectly, from warfare, disease, and famine.
Religious Conflicts in Asia:
The Taiping Rebellion (1850-1864): A millenarian movement in China that resulted in an estimated 20-70 million deaths.
The Boxer Rebellion (1899-1901): A violent anti-foreign and anti-Christian uprising in China that resulted in an estimated 100,000 deaths.
These represent only a fraction of the religious conflicts throughout history. The total number of people killed in the name of a god is likely in the hundreds of millions, if not more.
I agree, there are a number of factors that are involved, but everyone believes that their version of god is on their side.