Yes, it's an almost unknown aspect of rural France, but thanks to researchers, we had means to discover this cast system in Western Europe.
But this cast system has also reached the US with french migrants leaving Europe. Several towns in the US are called LaPlace, like in Louisiana. LaPlace means "The place" or "The location". This name was the one given to the cagots villages : it means their villages had no name. Cagots also didn't had family names. When some of them migrated to America, they told the US Immigration Officer that their family name was Laplace or Cagot.
The US had no knownledge about this, so this cast system didn't took place in the US. Also, the US only saw that the cagots were Whites christians, which was above other races, even if they were speaking english very poorly. However, the US had the habit of migrants speaking english very badly, so it wasn't exceptional either.
But, yeah, this his hypergamy and an extreme cast system, identical to the ones in India, maybe worse.
Even if it wasn't cagots people, very recently, we were astonished to discover that a similar cast with 3000 members was existing in the center of Paris. They call themselves "La Famille" which means "The Family", they live in a whole building block they bought little by littlte, and they live like this at least since 1892. They have no right to marry someone outside the Family. They never speak about the Family, like in the movie Fight Club. Due to them only marrying between their own small community, their consanguinity is astronomical. However, there can be zero Incel in such a "group", because every man is married. In fact, there are more females than males in The Family, leading to many females having no guy to marry with. As they can't marry outside, they stay single and are called "The Aunts".
Too bad the Wikipedia French page about them wasn't translated in english yet. I found this very fascinating. I've always been fascinated by secluded social groups.