I'm quoting some portions from lectures and discourses of Swami Vivekananda that may be useful regarding the question and may partially answer it.
From THE GREAT TEACHERS OF THE WORLD:
The nation goes down, and everything seems to go to pieces. Then, again, it gains strength, rises; a huge wave comes, sometimes a tidal wave — and always on the topmost crest of the wave is a shining soul, the Messenger. Creator and created by turns, he is the impetus that makes the wave rise, the nation rise: at the same time, he is created by the same forces which make the wave, acting and interacting by turns. He puts forth his tremendous power upon society; and society makes him what he is. These are the great world-thinkers. These are the Prophets of the world, the Messengers of life, the Incarnations of God.
The vibration of light is everywhere in this room: why cannot lie see it everywhere? You have to see it only in that lamp. God is an Omnipresent Principle — everywhere: but we are so constituted at present that we can see Him, feel Him, only in and through a human God. And when these great Lights come, then man realises God. And they come in a different way from what we come.
From MY MASTER:
The next desire that seized upon the soul of this man as to know the truth about the various religions. Up to that time he had not known any religion but his own. He wanted to understand what other religions were like. So he sought teachers of other religions. By teachers you must always remember what we mean in India, not a bookworm, but a man of realisation, one who knows truth a; first hand and not through an intermediary. He found a Mohammedan saint and placed himself under him; he underwent the disciplines prescribed by him, and to his astonishment found that when faithfully carried out, these devotional methods led him to the same goal he had already attained. He gathered similar experience from following the true religion of Jesus the Christ. He went to all the sects he could find, and whatever he took up he went into with his whole heart. He did exactly as he was told, and in every instance he arrived at the same result. Thus from actual experience, he came to know that the goal of every religion is the same, that each is trying to teach the same thing, the difference being largely in method and still more in language. At the core, all sects and all religions have the same aim; and they were only quarrelling for their own selfish purposes — they were not anxious about the truth, but about "my name" and "your name". Two of them preached the same truth, but one of them said, "That cannot be true, because I have not put upon it the seal of my name. Therefore do not listen to him." And the other man said, "Do not hear him, although he is preaching very much the same thing, yet it is not true because he does not preach it in my name."
That is what my Master found, and he then set about to learn humility, because he had found that the one idea in all religions is, "not me, but Thou", and he who says, "not me", the Lord fills his heart. The less of this little "I" the more of God there is in him. That he found to be the truth in every religion in the world, and he set himself to accomplish this.
Thus, according to Vivekanada yes, fundamentally all comes from the absolute truth and when people say they're not same or fight among them are either due to politics or due to ignorance that they don't know the true meaning of Dharma and God.