Well, I have thought a great deal about this, having traveled many times to places where there is one predominant and often governmentally-supported form of Christian faith (such as Mexico, England, France, Spain and also Serbia, Poland, Croatia and lately Russia and Belarus). In countries where there is one predominant (and dominating) religious expression you end up seeing one of two things happen: 1) the church becomes so entangled with the state that it uses political power to further its own political ends, persecuting others of different faiths and even different expressions of the same faith in Jesus; or 2) the church becomes largely irrelevant to modern life and, even if still supported by state funds, is largely dead and empty. In Western Europe things largely have gone this second direction, while in Eastern Europe largely in the former direction. Of course, there are exceptions, but in general, while unity in the church is something Paul seems to value highly in Ephesians 4, on national scales it seems to lead to church death or corruption and widespread nominalism. In fact, I cannot really think of a counter example, where a unified church expression leads to spiritual vitality.
The war has made evangelism in Bosnia especially difficult, say in comparison with other Eastern European countries. The IFES team talks with nominal Muslims all the time (it is their primary activity) who are unhappy with their life or have questions or are willing to dialogue about God. But they are not very likely to consider the claims of Jesus: after all, Jesus is the guy that the Orthodox Serbs and the Catholic Croats claim is their Lord, and they are the ones who were shelling and sniping at them during the war. (As our host said, there were really no good guys during that war, but the Serbs were the early aggressors.) So evangelism has gone very slowly, in part because of the close identification of ethnic identity and religious faith. Muslims can't convert because it isn't just a matter of individual conscience and choice, but of group identity and loyalty, and the other side is the most recent historical aggressor.
I will think more about the implications of the lessons learned by evangelical Christians about ministry to Muslims after what is perceived of as a war between Christians and Muslims (that may continue to have relevance for Americans as we think of the foreign policy implications for ISIS and other threats in the Middle East). But I don't have more on that topic now.
But I am left with my observation that institutional unity in the Church doesn't often produce peace and tranquility, but quite the opposite. So I am actually happy with the American Church being at odds about all sorts of things, and with hundreds of denominations and thousands of independent churches. I think it brings healthy competition to the spiritual marketplace, and it at least is one of the things that has kept the American Church, for all its many faults, dynamic while in most places in the Western world the church is in rapid retreat. (And for those who want to point out that the Church in Africa is even more fractured and more dynamic, I would only say, Yes! and Amen!)