I just learned the other day that the Visigoths and most Germans who originally converted to Christianity converted as Arians which means they didn't believe in the holy trinity. They believed Jesus came from God but wasn't God.
Truthfully, this is what I've always believed about Christianity also but I never knew the term was Arian or that it was a fairly popular belief until the Catholic Church forced everyone to convert to the Holy Trinity belief system.
And if you see a map of genetic clustering across world populations, you see that the middle east and europe are closer to each other than any other 2 populations. Closer even than mongoloid populations:
https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Whole-genome_based_PCA_and_clustering_of_worlds_ethnic_groups.png/500px-Whole-genome_based_PCA_and_clustering_of_worlds_ethnic_groups.png
Particularly, all of these groups descend from somewhere in the Caucasus. Whether it's Anatolian farmers, natufians, Iranian hunter gatherers, western hunter gatherers, caucasian hunter gatherers (obviously), or even ancient north eurasians, which were a splinter from the same ancestry as WHG that mixed with a tianyuan element not related to west eurasians in Siberia.
In a nutshell all of these groups started leaving the area of the Caucasus (and also around Iran and Asia minor) at around the end of the ice age.
But there are 2 groups of people that throw a wrench into this and have stopped us from being, well, completely the same groups of people. Even though Europeans and middle easterners have both to some extent, it's in wildly different amounts:
The Arabs have basal eurasian dna thats much less present in Europeans that was brought by the natufians (the other half of natufian dna is from a population descended from WHG)
Europeans have basal east Asian dna that is effectively nonexistent in Arabs that was brought by the yamnaya which has its roots in the eastern hunter gatherers and therefore from ancient north eurasians, they mixed with tianyuan as I said earlier (indeed haplogroup R is an east Asian haplogroup in origin)
And of course, there was some mixing with unrelated local hunter gatherers of people who were in those areas that are not named.
A small amount of completely unrelated genetics throws off the genetic clustering. But only slightly. Indeed on a chart of world population genetic clustering, one would be forgiven for thinking that the middle east is in Europe. And these are modern populations. Imagine the iron age, which is when Islam spread. Let's go back a bit further and imagine the bronze age while we're at it.