Short answers, pulled from the story.
Protestantism is a form of Christianity that emphasizes justification through faith alone, salvation by unmerited divine grace, the priesthood of all believers, and the Bible as the sole infallible source of authority. Its core beliefs are summarized by the five solae. Protestants follow the theological tenets of the Protestant Reformation, which began in the 16th century.
Martin Luther began the Protestant Reformation when he allegedly nailed his Ninety-five Theses to the door of the All Saints' Church in Wittenberg on the 31st of October 1517. The theses reacted against abuses in the sale of indulgences by the Catholic Church.
The name comes from six princes of the Holy Roman Empire and rulers of fourteen Imperial Free Cities who issued a protest against the edict of the Diet of Speyer in 1529. They were the first individuals to be called Protestants, and the term was initially political before acquiring a broader religious meaning.
The five solae are sola scriptura (scripture alone), sola fide (faith alone), solus Christus (Christ alone), sola gratia (grace alone), and soli Deo Gloria (glory to God alone). The Latin word sola means alone, only, or single, and the phrases emerged during the Protestant Reformation to summarize the reformers' beliefs in opposition to Catholic teaching.
The largest Protestant denominational families include Lutheranism, Anglicanism, Calvinism or Reformed Christianity, Methodism, and Baptists, along with Hussitism, Adventism, Pentecostalism, Quakerism, and the Plymouth Brethren. Lutheranism has approximately 80 million adherents, the Anglican Communion has 85 million, and Pentecostal and Charismatic Christianity together number over 500 million.
Lutheranism spread from Germany into Denmark-Norway, Sweden, Finland, Livonia, and Iceland, while Calvinist churches spread in Germany, Hungary, the Netherlands, Scotland, Switzerland, France, Poland, and Lithuania. The political separation of the Church of England from the Catholic Church under King Henry VIII began Anglicanism. The printing press invented by Johannes Gutenberg and Bible translations into native languages helped carry Protestant ideas across the continent.
The St. Bartholomew's Day massacre took place in August 1572, when the Catholic party killed between 30,000 and 100,000 Huguenots across France. It was the most intense moment of the French Wars of Religion, which eventually ended when Henry IV of France issued the Edict of Nantes.