Gibbon's monumental work is an excellent reference for the Crusades. Gibbon had a favorable impression of Muhammad and the early Islamic civilization, and he often showed how the Muslims had better ethical behavior than did their Christian opponents.
I have not yet had time to make a strong case for universal salvation. Just let me state, for the interim, that two great contemporary Christian thinkers have repudiated the belief in eternal punishment, at least by inference. I would like to bring two excellent books to your attention:
1. The Faith of a Physicist, by John Polkinghorne.
2. The Desire of the Everlasting Hills, by Thomas Cahill.
Polkinghorne is an Anglican clergyman and also a nuclear and particle physicist in the United Kingdom. He shows how the Christian faith, as summarized by the Nicene Creed, is consistent with the scientific outlook. Cahill is a well-known American author who has shown how various cultures, including Irish, Jewish, and Greek, have revolutioned world history. Jesus Christ is the "desire" alluded in this book, and Cahill shows how the ethical teachings of Jesus could yet change our world for the better.
I enjoy this forum, despite the unfriendly reception which I received from certain members thereon. Not all Christians are amiable individuals, but I try to live by the Sermon on the Mount.