The matter was complicated by the fact that Europe was no longer simply Christian. Christianity had lost its hegemonic control over European culture over the previous centuries and had been joined, if not replaced, by a new doctrine of secularism. Secularism drew a radical distinction between public and private life, in which religion, in any traditional sense, was relegated to the private sphere with no hold over public life. There are many charms in secularism, in particular the freedom to believe what you will in private. But secularism also poses a public problem. There are those whose beliefs are so different from others' beliefs that finding common ground in the public space is impossible. And then there are those for whom the very distinction between private and public is either meaningless or unacceptable. The complex contrivances of secularism have their charm, but not everyone is charmed.
Europe solved the problem with the weakening of Christianity that made the ancient battles between Christian factions meaningless. But they had invited in people who not only did not share the core doctrines of secularism, they rejected them. What Christianity had come to see as progress away from sectarian conflict, Muslims (and some Christians) may see as simply decadence, a weakening of faith and the loss of conviction.