How does the Roman Catholic Church connect the different European kingdoms of Medieval Europe?

Answer 1

There are many possible answers to this question, but one way is that it united the people against common enemies. Since all of Western Europe at the time was Roman Catholic, they all believed in the same God, and they had the same traditions. This eventually led them to demonize the same people. Jews, Muslims, and heretics are such groups that were demonized by the church. This unification against these enemies eventually led to both inquisitions in France and Spain, as well as crusades to the holy land.