The history of mankind is filled with numerous instances of violent bloodshed because of the attitude of 'My God alone is true'. Swami Vivekananda explains very graphically how this syndrome came about and how India was fortunate to escape this fate of religious exclusivism. Swamiji says:
We observe in the histories of Babylon and among the Jews an interesting religious phenomenon happening. We find that each of these Babylonian and Jewish peoples was divided into so many tribes, each tribe having a god of its own, and that these little tribal gods had often a generic name. The gods among the Babylonians were all called Baals, and among them Baal Merodach was the chief. In course of time one of these many tribes would conquer and assimilate the other racially allied tribes, and the natural result would be that the god of the conquering tribe would be placed at the head of all the gods of the other tribes.
Thus the so - called boasted monotheism of the Semites was created. Among the Jews the gods went by the name of Molochs. Of these there was one Moloch who belonged to the tribe called Israel, and he was called the Moloch-yahveh or Moloch-yava. In time, this tribe of Israel slowly conquered some of the other tribes of the same race, destroyed their Molochs, and declared its own Moloch to be the Supreme Moloch of all the Molochs. And I am sure; most of you know the amount of bloodshed, of tyranny, and of brutal savagery that this religious conquest entailed. Later on, the Babylonians tried to destroy this supremacy of Moloch-yahveh, but could not succeed in doing so.
It seems to me, that such an attempt at tribal self-assertion in religious matters might have taken place on the frontiers of India also. …but India's history was to be otherwise… For one of the greatest sages that was ever born found out here in India even at that distant time, which history cannot reach, and into whose gloom even tradition itself dares not peep — in that distant time the sage arose and declared, "He who exists is one; the sages call Him variously – Ekam Sat Viprah Bahudha Vadanti" . This is one of the most memorable sentences that was ever uttered, one of the grandest truths that was ever discovered. And for us Hindus this truth has been the very backbone of our national existence. For throughout the vistas of the centuries of our national life, this one idea comes down, gaining in volume and in fullness till it has permeated the whole of our national existence, till it has mingled in our blood, and has become one with us. We live that grand truth in every vein, and our country has become the glorious land of religious toleration. It is here and here alone that they build temples and churches for the religions which have come with the object of condemning our own religion. This is one very great principle that the world is waiting to learn from us. Ay, you little know how much of intolerance is yet abroad. It struck me more than once that I should have to leave my bones on foreign shores owing to the prevalence of religious intolerance. Killing a man is nothing for religion's sake…
Therefore the world is waiting for this grand idea of universal toleration. It will be a great acquisition to civilisation. Nay, no civilisation can long exist unless this idea enters into it. No civilisation can grow unless fanaticism, bloodshed, and brutality stop. No civilisation can begin to lift up its head until we look charitably upon one another; and the first step towards that much - needed charity is to look charitably and kindly upon the religious convictions of others. Nay more, to understand that not only should we be charitable, but positively helpful to each other, however different our religious ideas and convictions may be. (CWSV, vol. III, pp. 185-188.)