So one of the fun things about generations of endogamous marriage (marrying within your group) is that it leads to a “background” level of relatedness with people you don’t know.

So in Ashkenazi communities that still do arranged marriage, they often do genetic testing first - because even without knowing each other, a bride and groom could possibly have a genetic closeness equivilant to maybe cousins.

A lot of communities in India show this phenomenon too.