In the beginning, by which I mean before 1054, the Church was united, though the Eastern and Western pieces had lots of theological differences, which they could just not iron out. But then it was 1053, and the Patriarch of Constantinople closed all the Latin churches in the city, and after that, the Pope of Rome tried to get the Patriarch to recognize him (the Pope) as the head of the Church, which he wouldn't, and then they excommunicated each other, and we had The Great Schism of 1054. But there was still lots and lots of trade between the East and the West, because money, which is why in 1182 there was a large Italian population of traders and their families in Constantinople, especially since they'd been given lots of economic incentives, and so they were making lots of money and shouldering all of the Byzantine traders out, and also, alas, the Italians were VERY arrogant and annoyed everybody, besides which they were very badly behaved, and a mob that had been celebrating the entrance into the city of their new emperor Andronikos pivoted and began massacring all of the Italians they could find in the city. This was very bad. Very bad indeed. And it didn't help the East-West relations, which would be reaching their nadir with the Sack of Constantinople in 1204, after which the East and the West wouldn't even speak to each other, for hundreds of years. We explain the massacre and Michelle finds novels, including one by, I kid you not, Louis L'Amour, who apparently had a sort of cowboy take on the whole shebang.