Sriram,
I think your views are far too simplistic. You simply seem to concentrate on one thing, religion, which, of itself, can be a particularly divisive product, and then seek to suggest that its unifying force is illustrated by the fact that four major religions became the dominant forces. I would suggest that, in contrast to this, such things as increasing trade between countries and communities, urbanization, increasing democratization, the influence of the 'enlightenment' period on humanistic thinking, greater communication, and the means of communication, have all had their important parts to play here. And, of course, even with religion, there are many disparate groups within them which has led, and continues to lead to conflict. In other words, for every unifying aspect of these dominant religions(although I'm not sure that Buddhism really counts), there is a darker, more divisive side which can be seen to have its influence on many of the conflicts of today.