I stumbled onto an interesting paper by David A. Plaisted, professor of computer science at the University of North Carolina Chapel Hill, which discusses the estimates of dead from the Inquisition. Perhaps most striking was this quote:

Bertrand, the Papal Legate, wrote a letter to Pope Honorius, desiring to be recalled from the croisade against the primitive witnesses and contenders for the faith. In that authentic document, he stated, that within fifteen years, 300,000 of those crossed soldiers had become victims to their own fanatical and blind fury. Their unrelenting and insatiable thirst for Christian and human blood spared none within the reach of their impetuous despotism and unrestricted usurpations. On the river Garonne, a conflict occurred between the croisaders, with their ecclesiastical leaders, the Prelates of Thoulouse and Comminges; who solemnly promised to all their vassals the full pardon of sin, and the possession of heaven immediately, if they were slain in the battle. The Spanish monarch and his confederates acknowledged that they must have lost 400,000 men, in that tremendous conflict, and immediately after it-but the Papists boasted, that including the women and children, they had massacred more than two millions of the human family, in that solitary croisade against the southwest part of France.

— Bourne, George, The American Textbook of Popery, Griffith & Simon, Philadelphia, 1846, pp. 402-403.

Full pardon of sin and possession of heaven if they were slain in battle? That sounds scarily familiar…