Where did you get such nonsense? St. Sylvester I was pope during the Council of Nicea in 325. No emperor ever served as pope.
You ignore the Albigensians (Over the twenty year period of this campaign an estimated 200,000 to 1,000,000 people were killed).
Albigensians were not Christian. Read up on them before you respond.
John Huss, a Bohemian preacher of reformation, was burned at the stake on July 6, 1415. Pope Martin V issued a bull on 17 March 1420 which proclaimed a crusade "for the destruction of the Wycliffites, Hussites and all other heretics in Bohemia".
The Hussites had already destroyed the Churches and monasteries and slaughtered the Catholics of Bohemia. This was my original post:
"For 1500 years, the Catholic Church authenticated its teaching by reference to its scripture in the context of history. No Christian ever thought to question this basic understanding of reality."
Neither the Albigensians nor Hussites were Protestants. Are you saying these groups were Christians who questioned teaching according to history?
The Crusades in the Middle East also spilled over into conquest of Eastern Orthodox Christians by Roman Catholics and attempted suppression of the Orthodox Church.
The sack of Constantinople of by Crusaders was strongly opposed by the pope but he could not control the soldiers at a distance. It was a great tragedy, but the city had a massive collection of wealth and no fighting men to defend it. Westerners at the time kept up their fighting skills by frequent wars. No pile of treasure in the West would have survived if left undefended.
That might be true but Constantine certainly did his part of the first ecumenical council in Nicaea. Constantine invited 300 bishops to attend, with all expenses paid. He also gave the Bishops their opening instructions. He was VERY involved in Nicaea. Rome and religion were working very closely together for the same end result. Keeping Rome powerful, if not by politics, then by religion. The same thing they enjoy today, a political system state, and a religious state. Each side saw the value in the other side and a pact of convenience was arranged. Never mind that Roman paganism found its way to the Catholic Church. That too was conveniently merged together. And so it's been down the years, until lately, voodoo is the new paganism finding its home in Rome.