Judaisms Argument for Validity of God

I’ve always asked how someone can believe in the Old Testiment and know it really came from god and all the mircales depicted in it occured. The reply I get for its validity is that it was givin before an entire nation. Muhommad used to go to a cave and come back with divine revelation. Jesus’s mircales were only witnessed by a hand few of his diciples, same as Buddah, however according to the Old testiment god came before the entire nation of the Isrealites.

You see its not so hard to pass of a lie if one person writes it down or several people conspire to do so, but I’d imagine it would be quite difficult to do so before something like 2 million I think it was. I mean the Old testiment proclaims god to be amongst the entire nation of people and mircales to be happening everyday before them; to manefest such a lie amongst so many sounds implausible does it not?

Look we could get several of us together and conspire and make a cult or new religion but we’ll only have our word to testify for it. How do you explain an entire nation doing something of the same sort?