I am mostly concerned with things that immediately affect me, but...
Suppose you look at the headlines in world news today, an article would be on the Sri Lankan army defeating the LTTE rebels and another would be Barack Obama and Binyamin Netanyahu meeting up to talk about Israel and Palestine. The issues being a separate state for the Tamils in Sri Lanka and a separate state for the Palestinians in Israel. More examples off the top of my head - in India, an independent state of Kashmir, in the UK, an independent state of Northern Ireland.
What do all these conflicts have in common? A group of people who want a place for themselves, want their voice heard, don't think they belong. In Sri Lanka, its for the Tamil minorities who don't have enough representation and are marginalised. In Israel/Palestine, its a fight for the state of Palestine, a state for the Muslims separate from that for the Jews. In India/Pakistan, its now a group of people who want to be separate from both India and Pakistan. In the UK, its a group of people who want an independent state of Northern Ireland.
Why the separatism? Ethnicity (Tamil vs Sinhalese), religion (Jew vs Muslim, Hindu vs Muslim), sect (Catholics vs Protestants), politics. Why do people care? Why do they care so much that they are willing to die and kill for it? We kill for money, for power, for political reasons - there is no solution to conflicts resulting from those interests. But we also kill for the belief that our way of life is different and needs protection/representation, and in revolt against oppression/bullying by other people/countries. You can only push your views on a person/set of people/nation so much before they revolt/rebel. There will always be majorities and minorities, people who identify themselves as one or the other, people with blind faith that their way of life is the only one.
Too much faith, too much belief or too much of a sense of belonging is bad. It takes away level headedness and blinds you to other perspectives. In each group of people in each nation in each religion, there will be people who are nice and good natured and people who are arrogant, insensitive and rotten. In EACH of them. But there is something in most of us that makes us judge all others except ourselves when they are even minutely different from us. We somehow lose the ability to see that we are the same you and I. Well, basically.
But then on the other hand conflict is inevitable and even necessary. Its the people with intense faith/belief who lead others. They have definite views, definite visions on how they should be, how to make things better and they work for it and fight for it. In many ways, they lead to a better group of people, a better community, a better nation. And it would be great if all the views and beliefs matched and we could all just get along (quoting Jack Nicholson in Mars Attacks!) and build a great nation/world. But there will always be people with different views, and mostly they will be a minority and they will have to fight for having their say. If we all just are a little bit more accomodating, and open our minds a bit more, we could maybe all get along after all. There is a need for balance between having faith, believing in something, standing for something and bettering things and making sure that the 'bettering' is not at the cost of someone else's way of life, however minor that might be.