Can people please stop saying that recreational PIV is natural and normal, for the love of kittens? Read some anthropology. Before Western intervention, there were (and in some places still are) many, many cultures where there were extensive restrictions on where, when and how couples could engage in PIV. This was embedded into culture in the form of taboos or whatever else, and worked as a natural form of birth control to stop overpopulation.
So how did normalising of PIV come about in the West, and specifically in the expansive and militaristically powerful nation of Britain? Well, the British wanted an Empire, didn’t they? They needed to populate said Empire with lots and lots of bodies, didn’t they? So PIV was normalised as the only acceptable/legitimate kind of sexual contact via religious belief and cultural customs. This produced a massive surplus population (many of them poor) who could be lured onto the frontiers of Empire with the promise of riches and a better life.
Also note that once on the frontiers of Empire, Western men would perpetrate mass rape on local female populations as part of the business of colonisation, which was, in effect teaching the local populations to accept all-PIV/rape-all-the-time as ‘normal’. Very often this was further cemented through the work of missionaries who would impose Christianity and forbid the local Indigenous populations from retaining their own cultural and religious beliefs.
So, you know, we start off with men violently raping women using PIV so that they learn this is sex, and then once they have been sufficiently terrorised into submission, the level of force can sometimes decrease as now the female population accepts that it is normal and engages in it of their own free will, because they know what will happen to them if they don’t. And then the practice is further normalised through the imposition of male-centric culture that makes it almost impossible to question it on a conceptual level.
We have no way of knowing that Western European men did not originally break Western European women into widespread acceptance of PIV via the same method of raping us into compliance. It actually seems highly likely to me. Or perhaps it was the Romans who brought the practice with them to Europe when they conquered the Celts (remember what happened to Boudica and her daughters?) and it was subsequently adopted by the local men. Maybe this was even one of the techniques used in the original subjugation of women that occurred however many thousands of years ago during the creation of patriarchy and male domination.