Both Islam and Christianity varied wildly in their approach by region. Islam certain has many ‘conversion by the sword’ incidents, some lasting centuries of brutality, and Christianity, likewise, has plenty of periods of co-existence.

One of the core issues, I think, is that we generally think of European Christianity, whose history is largely intolerant until the Protestant Reformation, and even after that often quite brutal; whereas Christianity in the East and in Africa very often included institutionalized coexistence with other faiths.