As for the Crusades, the property was Christian before the Muslims claimed it. Don't forget the Muslims had overrun Andalusia, Malta, and more before the West started defending itself.
Of course, even the Muslims would have a hard time competing with the carnage of socialists in the 20th century.
The Inquisition was designed as a terror campaign that would intimidate and frighten those who would challenge the dictates of the Church on matters ranging from theology to matters of the physical universe. There were a few notable targets of the campaign, including Galileo who was threatened with agonizing torture for his scientific observations. The fact that there were no piles of bodies produced by the Inquisition only serves to prove that it was indeed a terror campaign meant to make "examples" of "heretics" -- one that was an official policy of the Church! One who is sufficiently hostile to Christianity could credibly, therefore, make the case that the Christian Church was essentially a terrorist organization for centuries, enforcing it's will by either force or fear. I will not go so far, however.
And let's not forget the many persecutions of fellow Christians who differed from the official theology of the Church. One of the most revolting examples of this barbarism was the Albigensian crusade against the Cathars of France in 1209. Simply because of their differing theological views, Pope Innocent III waged a crusade to convert them or eliminate them. Mass slaughters occured of women and children by Christian knights. One such slaughter at Béziers, resulted in the mass murder of not only Cathars, but plenty of Catholic sympathizers as well. The number of deaths were in the tens of thousands -- in the hundreds of thousands for the entire crusade. And while it is true that the great holocausts of the 20th century count deaths in the millions, it is also true that the population of the Earth exploded in the 20th century. The atrocities have to be compared on a relative basis, also taking into account advances in weapons technology that allowed for more efficient mass killing, as was pointed out by OWK.
And, by the way, I in no way implied that secular states and causes have not perpetrated carnage on vast scales. I am only insisting that those who condemn one religion for it's barbarisms should not forget those of their own religion.