The short answer to your question (a short answer) is that historically, religion has always been an identity-shaping force, something for a community of seemingly similar people to rally around and define themselves relative to others.
For example, we know that the only thing that allowed the Jewish people to survive as a coherent group, and not disappear into history like the Babylonians, Assyrians, Hittites, Amalekites, Chaldeans, Phoenicians, and the like, was their strict adherence to the practices of Judaism. If they had not done this the Jews -- apparently very similar to their neighbors in other respects -- would be unknown to us today. Judaism, then, was vital to identity-preservation.
The Crusades? I would argue that the folks who would become 'Europeans' thought something like this to themselves: 'As long as parts of this land is colonized by the Arab-Islamic forces, we are a defeated people serving a defeated God. We need to turn this around....'
The Inquisition in Spain, in the 15h century, was put on by a country that was not sure of itself. The leadership wanted to build a modern, unified country and they thought they way you had to do that was by enforcing a unified Catholic faith. It was not a simple matter of 'religious intolerance' without rhyme or reason. In time, the extreme vigor with which the Inquisition was pursued in Spain gave them a bad press internationally: 'If you have to do all that, you guys really must be infested with Islam!'
So, where one sees religious extremism (fundamentalism) you are looking at a community that is not sure of their identity. Indeed, if we ask the question: Why is there so much religious fundamentalism in the United States and hardly none in Europe? -- the answer I would give is: religion did its job in Europe after thousands of years, and they know who they are.
There is a way in which we, in the United States, still really do not know who we are as a nation. The ongoing, ugly legacy of the Civil War is a part of it.
When a community knows who they are and feels secure in this, they can let religious formality drop, and allow what you refer to as 'spirituality,' to flourish.
Take it easy. :D