One thing I don’t see mentioned is that up until 1054 AD, all Christians were Catholics. In 1054, the Eastern Orthodox broke off from the Catholic Church. Then the whole Protestant reformation started in 1517 with Martin Luther, a German Catholic Priest, was upset at the Pope and the Church for a variety of reasons, but the primary one being the Pope selling indulgences (free entry into heaven) to finance the building of St Peters Cathedral. The Pope didn’t like his rule being questioned (due to the Catholic belief in Papal infallibility, meaning if the Pope says or does it, it is right), so he excommunicated Luther (kicked him out of the Church). However Luther was extremely popular in Germany, so he still had a large group of followers that he continues to preach to. This group went on to become the Lutherans. Other religious leaders saw it was possible to nitpick certain Catholic beliefs, which led to many other Protestant churches forming like the Baptists, the Calvinists, the Anglicans, etc. This cherry picking of ideas has continued since then leading to hundreds of distinct Protestant sects. All of whom are still Christian, but vary in their specific ideology from other Christian sects, including whether or not other Christian sects will go to heaven or not.