Justin24 said:
Could all religions be inner connected?
Yes, and it isn't all that far-fetched, particularly to those who have studied anthropology and/or linguistics. No existing religion was created out of a vacuum; they are always an extension of an earlier religion of an earlier culture.
The trouble is that these connections have often occurred thousands of years ago. Some of them are almost literally on the edge of history and prehistory. Others can be derived by generally common deity names and theological similarities within each religion's scriptures. And, most certainly, the history of some religions are forever lost.
Despite their current hatred of each other, the Jewish and Muslim people share a common heritage, as demonstrated linguistically through study of Hebrew and Arabic. Both are designated as "Semitic" languages, and while the Bible likes to portray the Israelites as outsiders claiming their land from "outside enemies," linguistics and history have further demonstrated that they were, in fact, relatives within a larger Semitic family.
Where things get interesting is how Indo-Iranian beliefs get thrown into the mix. Hinduism, being one of the oldest known religions, had a schism during the early Vedic era, which led to Zoroastrianism, which was the state religion of the Persian Empire. And by the way of cultural imperialism, their theology profoundly influenced Judaism (through the Pharisees) and Christianity (both through the Pharisees' heritage and the popularity of Mithraism during the time of Jesus).
And, to add further into the mix, "Indo-Iranian" is merely a sub-family of the larger "Indo-European" family, thus expanding its heritage to all of Europe and Russia.
Now obviously, time has done a great job of obscuring these connections, not to mention the scriptures of many of these religions; after all, a schism usually makes the old religion an enemy of the new religion, so they are quick to try and erase all connections. However, the connections are there, wide open to those who know where to look.