Nationalisms

Talking to Moustapha from the Chad is always thought provoking. I'll disagree with much of what he says, yet there's a lot of sense in his words. When he talks about homosexuality being wrong and how it's a crime in his home country, this disturbs me, but at the same time he has a very humanistic approach to life, even if he is a 'practicing' (in a sub-saharan kinda way) muslim.On this note, I find it interesting how he calls himself a religious believer with humanistic beliefs, while I would describe myself as a humanist who agrees with many christian(since that is my culture)beliefs.
What made me want to post about him, was when he said that too often people took religion(and here he was talking mainly about Islam, obviously)as a hereditary concept, while he believed one cannot be born a muslim.
What I wanted to know, in my western cliche manner, was if he described himself first and foremost as a muslim or as a Chadian or African. I felt there was no straightforward answer to this question. I would have expected him to say 'muslim', yet this was not so obvious to him.
As an African, his culture and nationality were at least as important as his faith, and he made comparisons between Chadians and other African nations such as Camerounians and Nigerians, saying his people showed more solidarity among one and other. On the question of a worldwide muslim nation, he was much more vague. I don't think he really felt as strong a bond with muslims from other cultures. Both him and the other 'Moussa' have quite strong anti-arab feelings(even if they have arab friends!).
Culture obviously has a strong role in determining the way people view and practice their religion.At the same time, Moustapha claimed there could be only one 'Islam'. Yet, Islam was brought to his people by the arab invaders. So whose 'Islam' is right? It's like the clash between european and african Christianity.
My question is, can organised religion and culture coexist? Is nationalism a substitute for religion, or do they go hand in hand?
To me, these two concepts contradict each other, and yet are routinely used and abused together by leaders in order to dupe the masses. My humanistic faith is universal, as is supposedly the Christian faith, and as such it cannot cohabit with nationalistic beliefs.