If we define Christianity as any group who teaches belief in Jesus, then not just Catholicism, Jehovah's Witnesses and Mormonism would be Christian, but Islam as well. Jesus is regarded as one of the holiest prophets in Islam.
What I'm defining Christianity as in my message here is belief/adherence to the original teachings of the Bible, as taught by Jesus and his biblical followers. Which does cast sharp criticism on the crusades. Jesus taught that all who live by the sword shall die by the sword. He led his example by submitting to the authorities of the land, without lifting so much as a finger against them. He also prophesied that Jerusalem would soon fall, and that the temple would be destroyed, and in 70 AD, it sure enough did as a result of the failed Jewish rebellion against Rome. The Holy Roman Empire in a similar way suffered a crushing defeat as a result of the Crusades and fell into ruins.