So I'll focus largely on the religious conflict that's occurred in Europe for the last six centuries or so, while acknowledging that religious conflict is pretty much a historical constant. This answer got a little wordy, so my apologies, the question you posed was just very broad.

For a very long time, most of Europe fell under the Catholic church which was centered in Italy - or what we'd recognize as Italy at least. The Catholic church was in fact the strongest overarching power in Europe at the time and had a great amount of wealth. This was collected from a number of sources, one of which was something called Indulgences. Essentially the idea was that people could give money to the Church - which I will use to refer to the Catholic church exclusively - in exchange for lessening the sin on their soul. As one can imagine, this was easily abused as the Church collected money from the rich who wished to, well, not rot in hell.

Indulgences have been around since the Middle Ages, if not earlier, and it's important to note that there were certainly other people who had issue with them but they were a core part of Martin Luther's Ninety-Five Theses. The Theses were basically a list of concerns that Luther had with the Catholic church. Furthermore, the Theses were easily accessible to those who could read due to the rise of the printing press in recent years. This allowed the information to spread and the period known as the Reformation began.

During the Reformation, other forms of Christianity were created that are probably recognizable to people - Lutheranism, Protestantism, Calvinism, and other branches were brought up as counters to the Catholic church. The Church did, as the period suggests, go through with some reforms. However, individual kings and rulers of various kingdoms/nations across Europe did switch religions. The Holy Roman Empire, which existed in the general area of Germany before Germany existed, was basically a collection of kings who controlled states, with the north more Protestant and the south more Catholic.

This became an issue when Ferdinand II was placed into position as the emperor of the HRE and tried to impose religious unity onto the entire collection of states. This prompted the Thirty Years' War which, in short, was at the time the most destructive war in European history. It permanently fractured the Church and increased nation-state sovereignty in religious matters. Importantly, it was the last major religious conflict in European history.

While religion does have ties to culture and political actions - for example religion in Eastern Europe, specifically Russia, has shifted thanks to its time under Communism - much of the present religious standards can be traced back to this time period. There are a few exceptions like England/The UK, which switched religions to the Church of England under Henry VIII and then had its own religious conflicts for the next few decades. The Age of Enlightenment also further weakened religious authority in Europe, but only in areas where the monarchs allowed for it... which further increases European religious variation. Interesting side note, but the US can thank the Age of Enlightenment for providing the basis for many ideas that the Founding Fathers would then take and bring to forming the early US government.

Anyways, I realize this only touches the tip of your question but I hope you can understand that it's a complicated topic and I'm sure that there are other perfectly viable answers. However the Thirty Years' War and the earlier Reformation period split the Catholic church in a way that it hadn't been since the Eastern vs Western Catholic split. I also did not discuss the influx of Muslim immigrants/rise of Muslim population in Europe because that's a little out of my wheelhouse, so sorry.

Completely unrelated, I hope your econ final went well :D