"French kissing", does not necessarily stem from France. In France, it is referred to as 'baiser amoureux' (love kiss) or 'baiser avec la langue' (kiss with the tongue), even if in past times it was also known as baiser florentin (Florentine kiss).
This is what I read from Wikipedia, hope this offers some insight
I think it (the term) started with the American soldiers returning home from WWI. I think . . .or that may have been the other thing they learned, getting head. Anyway, those French gals taught them things they never knew.