It came from the Torah, and is still part of the Old Testament of the Christian Bible. It's a mark of the covenant between God and his people, the Hebrews. Gen 17: 1-14. I'll let you look that up.
It's basically a spiritual agreement to put yourself under Jewish law, sealed by a blood sacrifice. Jesus, was circumcised. The Catholics believes that Jesus' circumcision, as his first blood sacrifice, was the beginning of man's atonement.
Later, after Jesus, as Gentiles were being brought into this new faith offshoot (remember the first Christians had been Jews), there was a disagreement in Galacia over the necessity of circumcision. Paul argued that if circumcision was a covenant that places you under Jewish law, then faith in Jesus could do you no good because Jesus came to fulfill (bring to a conclusion) Jewish law. So if you agree to keep Jewish law, you agree to keep the whole law which puts you outside the grace of Christ. That's in the Book of Galacians, Chapter 5, I think.
In most European countries circumcision is 20% or less, mostly less. It's 80% in many North African countries. Also high in Malaysia and the Phillippines.
In the US, it's around 70%.
That's a function of two things, in my opinion. What I said before about having been settled so much by religious extremists European nobility were happy to get rid of because they were dangerous to stability. The more zealous and extreme a faith tradition is, the more authoritarian it's going to be, the more it's going to ignore Galacians and delve into Leviticus. Fundies and Uber conservatives over here fucking LOVE Leviticus. They can't quote a single red ink passage but can quote the entire book of Leviticus. And they often do. Praise Jeebus. Because warrior Jeebus came to fulfill (force everyone to adhere to whether they're a believer or not) Jewish law. They've been The Little Authoritarians Who Could since they landed on these shores and set themselvesto genociding the Indigenous population. Just like Jeebus said.
The other reason has to do with hygiene. This one isn't so much about what is true or not, but what is believed to be true. In our early frontier years, life was dirty and hard here. Infant mortality was high and childbed fever was a profound fear. Doctors weren't exactly a surplus, wise women had not yet adapted to the medicinal herbs on a new continent, and if you lived outside a village you were extremely isolated from help. Infections killed.
Women have more open reproductive systems than men.
And so, I believe it became "common knowledge" from that time that you were less likely to get UTIs, yeast infections, childbed fever, all the infections that can plague the female reproductive tract if your sexual partner was a circumcised man than if he was not. I believe that belief has been passed down matrilineal lines. I believe that because of some of the things I've heard the old women say in my youth from church and school. I had a few really really old teachers and of course the grandmothers and a few great grandmothers of my classmates. My own family did not publicly speak about such things.
My own grandmother had both her boys circumcised even though she didn't hold to that belief. She did so for the reason I stated in the previous comment, whether she believed it or not, she knew other people did and she didn't want her boys to be prejudiced against because of it. I've heard a lot of similar reasoning. And at a 70% circumcision rate, when I was pregnant and making decisions, I went through the same lines of thinking about it.
There's also the aspect of, if you don't circumcise your boys, are you really dedicated to raising a good, moral man or are you just leaving him exposed to the devil and demonic influence? Obviously this is bullshit, but if you think your kid is safe from regimented, authoritarian, zealous, crazy religious nutters just because their beliefs are whack, you might want to think a little more on that.
I'll remind you that Urchlint was shoved off the top landing of a 6 ft slide, backwards, by a little Catholic girl in her class because her mother had told her I was a witch. Why? She has seen me out collecting wild plants, for our hamsters, and there had been a disagreement. And that was all she needed to harass, attempt to intimidate, and maybe harm my kid.
Religious nutters around the world are and always have been a persistent threat to life and limb. They're a danger to their communities. Nothing new here. It's the same in America as it is anywhere else in the world. We're no different.
You're welcome to think we're as backwards as you want. Just remember, we came from your unwanted elements and so American extremes and backwardness is always a reflection of your own old world ones.