Let me present you a situation. There is an ancient kingdom of which we know nothing. This kingdom was invaded and subjugated. Now, the one who conquered it changed it's religion completely and wrote it's history in a way that the new religion existed always.
We land in a situation where archeology gives us only ruins, all old literature and all old references wiped out(sometimes violently) and the new country hates it's old culture. I am not talking about Christian Europe or Islamic Arabia. I am talking about Tibet.
One image is enough to tell you the extent to which Tibet divorced itself from it's past. This is Goddess Srin Mo, who is a personification of Tibet. When she resisted introduction of Buddhism into Tibet, she was pinned to the ground with Buddhist temples.
"To subdue her, they build a total of thirteen Buddhist temples, some of which still stand today in places like Bhutan, to pin her down on her back. Four in the inner realm of Tibet to pin her shoulder and hip. Four at the border areas, pinning her knees and elbows.
Four at the borders beyond to pin her hands and feet. And finally, one at the Jo-khang, symbolizing her heart and considered the center of Tibet. Thus Srin is subdued and Buddhism can reign over Tibet."