The conflict comes from the nature of both religions. Both assert that there exists
only one god, and that there is only one correct way to obey him. And (unlike the third monotheistic religion, Judaism, which is a religion of one tribe, the "chosen people", Christianity and Islam are religions of all mankind, so they encourage conversion of all people to ...
Just a partial answer here to one of the questions posed in the body (not in the title):
"Is it safe to assume that such marriages of marrying off a Christian
daughter resulted in their forced conversion to Islam, and that they
were not allowed to remain Christian?"
It was not always the case that the wife would convert to Islam, at least when the ...