The comment that the prior person was commenting on, if you re-read it, is what was it like in the past.

With Martin Luther posting his Ninety-five Theses in 1517, followed by the Edict of Worms in 1521, when the Reformation occurred, Europe indeed wat almost wholly Catholic.

After the Reformation, the Protestants were still almost identical to the Catholic Church. It's not like they started calling their god "Uglamtafreck", whose dog became the savior of the world.

Protestants and Catholics have more in common than dissimilarities. But this is not the first time this has happened. In 1054 AD, there was the Great Schism, where the Catholic Church and Eastern Orthodox split from each other. This was due to stupid little things, as religions usually are about. The Great Schism was caused by the procession of the Holy Spirit (Filioque), whether leavened or unleavened bread should be used in the Eucharist,the bishop of Rome's claim to universal jurisdiction, and the place of the See of Constantinople in relation to the pentarchy. The Filioque clause means that the words that the Holy Spirit proceeds "from the Father", without additions of any kind, such as "and the Son" or "alone". That's it. Omit 3 words, split the Catholic Church in half.

But even then, the Roman Catholic Church has more in common with the Eastern Orthodox Church.

Europe was never a federation, but there was travel and communication between them. Not many European people would travel to South Africa or India. But England is a short boat ride away from France, so there was a lot of trade. In 1066, when the Normans took over England, they still were dukes in France and were royalty there.

So while there was not a political federation, there sure was a common culture of sorts, however tenuous it might be in some places, stronger in other places.

Like the USA with the Pacific and Atlantic Oceans, and only one country to the north (canada) that we share a border, and only one to the south that we share a border(Mexico), the USA has an excellent barriers to conquest from others.

It was the same in Europe. There was a Sea to the south, the Mediterranean, nothing north of Northern Europe except cold, and the east was protected by the Ural Mountains which go from far north to the Artic Ocean down to Kazekhstan/Uzbekistan. The Caucasus Mountains protect invasions from Iran/Persia. The Isthmus at Constantinople and the Iberian Peninsula (Spain) have always been the weak spots, and indeed, those were the areas where most attacks on Europe emanated from. But luckly, the Iberian Peninsula is separated from the rest of Europe by the Pyrenees mountains. Muslims conquered Spain in 711 AD and held on to it for almost 800 years, until 1492 AD, when the muslims were finally expelled in the Re-Conquista (re-conquest) by Queen Isabella and King Ferdinand, who also sent Christopher Columbus to the west in that same year of conquering the muslims in Europe. Furthermore, many of the Muslim elite, including Granada's former Emir Muhammad XII, who had been given the area of the Alpujarras mountains as a principality, found life under Christian rule intolerable and emigrated to Tlemcen in North Africa. Which just goes to bolster the argument that the two cultures of christianity and islam are more incompatible than one christian nation with another. By the way, the muslims did try to conquer Europe, but were stopped by Charles "The Hammer" Martel in France. If he didn't do that, we might all be talking in Arabic right now. The muslims were defeated in Aquitaine at the Battle of Tours in 732, and the muslims never really tried again after that.

All the languages in Europe descended from the Proto-Indo-European language, and with that came certain cultural identities and commonalities passed down through generations. Language is very important in proscribing much in culture and that is very strong. Whereas Arabic is descendant from a proto-Semitic language.

There were many people that traveled throughout Europe. Obviously not the serf who were tied to the land, but certainly there was cross border communications.