"Millions of Christians" were not slaughtered by anyone, at any time, for any reason, in the late middle ages and Renaissance. Try reading a history not written by Jack Chick, Jimmy Swaggart, or John Foxe.
The only thing that killed millions of Christians in that timeframe was the Black Death, which didn't really discriminate much in matters of theology.
Can I read Alexander Hislop, Keith Green, E.H.Broadbent, Dave Hunt or any the unabridged historians? Or am I to adhere to the Popes list?
Can I read the witness from a man my age who remembers the steel cages hanging outside the (I think) Cologne Cathedreal in which Christians were left to freeze or starve to death?
If it weren't for people like these and especially Jack Chick, the Jesuits would have that histpory of the Whore's shame completely expiurgated by now.
Don't be brainwashed.