I'm not downvoting you, but I do disagree with your hypothesis. In Europe religious power was heavily conflated with political power. Rome, through Catholisism

I'm not downvoting you, but I do disagree with your hypothesis. In Europe religious power was heavily conflated with political power. Rome, through Catholisism, remained the symbol of political legitimacy well into the Middle ages, and into the modern day. Especially in England where the Catholic / Protestant battle raged one way and other for hundreds of years, determining who should be king/queen, who the aristocracy were, who were worshiping in secret and so on. In our time we see this playing out in Northern Ireland, where issues of nationalism (English, Irish) are proxied into issues of religion (Catholic and Protestant). The concept of separation of church and state would happen in the US specifically because most immigrants there were fleeing state-sponsored religious persecution. They wished to create a place of religious tolerance, which alas has been somewhat imperfect in execution.