Protestantism is one of the three major divisions within Christianity (or four, if Anglicanism is considered separately) together with the Eastern Orthodox Church and the Roman Catholic Church. The term is most closely tied to those groups that separated from the Roman Catholic Church in the sixteenth-century Protestant Reformation.
The doctrines of the various Protestant denominations vary, but nearly unanimous doctrines include justification by grace through faith and not through works, the priesthood of all believers, and the Bible as the ultimate authority in matters of faith and order.
In the sixteenth century the followers of Martin Luther established the evangelical churches of Germany and Scandinavia. Reformed churches in Switzerland were established by John Calvin and more radical reformers such as Huldrych Zwingli. Thomas Cranmer reformed the Church of England and later, John Knox established a more radical Calvinist communion in the Church of Scotland.
The arrival of Grantville brought many new strains of Protestantism to 17th century Europe. One, the Baptist movement, had already begun as an English Separatist movement, but it was small and largely unknown outside of England; down-time Germans tended to view it as a form of Anabaptism. Most others, however, had arisen in the intervening centuries, founded by people who, thanks to the butterfly effect, would never exist.
Some strains of up-time Protestantism, such as the Baptists, Methodists, Disciples of Christ, and Church of Christ, had active churches in Grantville. Some others had a relative handful of members who had gone to churches in nearby towns. Others would only be known, if they ever were, from information in Grantville's libraries.
Strains of up-time Protestantism that wanted to try to retain their identities in the long run faced several issues. One was that they had been reduced to anywhere from a few hundred to a few dozen members, centered in one small town. Also, with the exception of Pentecostalism, up-time Protestant churches with no down-time analogs had little appeal to down-timers. As of 1636, most had apparently not made significant efforts at reaching out to the down-time population.