First of all you must know what really is religion.Then i am sure you will know how did religions spread.
Please read this for clearance:
We will have to understand that religion, the word 'religion' means two things.One, religion as we know it. And what do you know religion as? You know religion as Hindu religion, Muslim religion and even in Hindu religion there are so many sects. You can be a Shaiv, a Vaishnav, a worshiper of Sai Baba, a Kali bhakt. And there are so many religions in the world. These religions are nothing but organized belief system. Obviously, these religions have very little value because they are just belief systems. These systems have very little value. And what did we say? That belief will not allow you to see the truth. The religion that we commonly see around us is as in temples, in festivals, in fairs, on all the religious channels on television. There are so many religious channels on television these days.
There is this period of nine days(referring to Navratri), you must fast during these nine days. There is this period of thirty days (referring to Ramzan), you must fast during these thirty days. There is this festival and you must worship this god or goddess. That is one way of looking at religion. This religion is nothing but as an organized belief system, which has been handed to you by somebody else. This obviously has very little value. A free mind, an intelligent mind cannot accept this version of religion. That is why this version of religion is disappearing from the most developed and educated societies.
The very concept of religion is disappearing from some places. Are you aware that as much as 40% of Japan's population says that it does not believe in any religion? The number of atheists in US is rising day by day. They say that we do not follow any religion because the more one gets educated, the more one develops dislike for this kind of religion, where you are worshipping snakes. Recently, you had that festival where you worship snakes, where you are killing animals in name of sacrifice.
In the name of religion, if you do such stupid things, no educated mind will tolerate it. So that is the reason why the concept of religion is disappearing from certain places. This is the first version of religion.
There is however another religion and that religion is extremely important. The first is religions and there are at least three hundred active religions on earth today and there are numerous religious sects. The first is religions, organized belief systems. The second is religion. Just as science is one and truth is one, religion is also one. This second kind of religion has no adjective attached to it. It is not Hindu, not Muslim, not Sikh, not Christian, not Buddhist. It is just religion and that religion means intelligence. That 'Religion' means is 'Dharma'.
This are the excerpts from my blog Words into silence(Prashantadvait.com). Do visit for more clarity on this topic.