I once had a discussion with a friend who insisted that 'religion is not ethnicity'. It started me wondering if that is really true. In some parts of the world, ethnic groups seem to be defined by religion as much as 'race' or language. For example, we now think of someone who is 'Greek' as speaking Greek, and as someone who is 'Turkish' as speaking Turkish. But when Greece first gained its independence, and the two populations were intermingled in both Greece and Turkey, 'Greeks' were defined as Orthodox Christians, while 'Turks' were defined as Muslims. Language was secondary; so that someone who was Christian but spoke Turkish was defined as 'Greek', while someone who was Muslim but spoke Greek was a 'Turk'. That definition still persists today, and Greece claims that Albanian-speaking Christians in southern Albania (where the majority are Muslim) are actually 'Greeks'.
More recently, in Bosnia, when the 3 main 'ethnicities' were fighting, what really distinguished them? They all spoke the same language and shared virtually the same culture, living together for centuries. But the Croats were Catholic, the Serbs were Orthodox, and the Muslims were, of course, Muslim. If a Croat converts to Orthodoxy, is he then a Serb? How about a Muslim who becomes Catholic? Is she then a Croat? In Bosnian society, religion is not a flexible thing- a mere matter of personal conscience. It is almost a betrayal of one's community. In fact, Muslim communities throughout the Balkans are often seen by the Christian majority as 'collaborators' who betrayed their compatriots and converted for personal gain. (Whether that was true or not, centuries ago, the present generation can hardly be blamed for it.)
In Iraq today, most commentators refer to Shiites and Sunnis as if they are two ethnic groups- which, in essence, they are- but defined by religion, not physical characteristics or language, as both groups are Arabs. Even where there is a conflict between two truly distinct 'ethnic' groups, religion is still, often, a factor. Armenians and Azerbis speak different languages and have very different cultural traditions, but it is the religious factor- that Armenians are Christians and Azerbis Muslim- that has made the conflict in Nagorno-Karabakh so bloody. Similarly, in Sri Lanka, the Tamils and Singhalese speak different languages, but they are also of different religions: Hindu and Buddhist, respectively. Would their conflict have been so violent and unresolvable if they were of the same religion? I wonder.
The examples of religiously-defined ethnic groups are numerous: Sikhs in India, Maronites and Druze in Lebanon, Jews everywhere, and Mormons in the United States. Even in Canada, part of the 'French Canadian' identity is their Catholic heritage. The concept of religion as a matter of personal conscience, unrelated to an individual's status in his community, is historically recent, and a result of the humanism and individualism which emerged in Europe after the Reformation, and during the Enlightenment. Unfortunately, it has not been universally accepted, as we saw recently in Afghanistan, with the Muslim who converted to Christianity. In parts of the world where Christians and Muslims, or Muslims and Hindus, or Protestants and Catholics (N. Ireland) are killing each other, simply for being of a different religion, it's not exactly surprising that anyone who converts is looked at with suspicion. As long as religion continues to be used to define who is "us" and who is "them"- who is "in" the group (and can therefore be trusted) and who is "out" (and must be feared), this will continue to be the case.