Before I get into Luther's 95 Thesis, the book I'm reviewing mentions several men who made what Luther accomplish possible.
Johannes Gutenberg: Without the printing press Luther's words and his challenge would have been only a local matter. Everything that Luther wrote and said was published and distributed through all of Europe. This was the major ingredient in the perfect storm of splitting the Church apart.
Desiderius Erasmus: Erasmus was a humanist, but his writings and work set the stage for the Reformation. He wrote against the excesses of the Church, but careful about getting too far under the Pope's skin. He compiled as many biblical manuscripts as he could find and buy and used them to compile a New Testament. It was these documents that Luther, and the King James scholars used to translate the bible into the vernacular (common language).
John Huss lived in Bohemia, modern day Czech Republic. He was a follower of John Wycliff of England. The Catholic Church of this day was divided between two Popes, the one in Rome and the other in Avignon, France. Alexander V in Rome controlled Bohemia.. Huss preached from Wycliff's writings and fought against Indulgences.
When the Church brought charges against Huss, he was given a Safe Conduct to attend his hearing. After he was condemned the safe conduct was revoked and he was burned at the stake.
His major crime was wanting to translate the New Testament into the Czech language.
Bohemia rose up in revolt and the Pope launched a crusade. A war was fought and the area was allowed to continue to follow the teachings of Huss. The teachings of Huss and the manner of his death would play a significant role in Luther's life and the Reformation.
Girolamo Savonarola lived in Italy and became significant in the city of Florence during the Renaissance. I used to tell my students that every party has an equal and opposite party pooper. The De Medici's ruled Florence and were patrons of the arts to some of the greatest artists of all time. There was money to lavish on splendid mansions and to decorate it with fine art. Quite a party. Then came the pooper: Savonarola was a monk who condemned the Medici's and the Pope for it's corruption and the sin of usury. The common people flocked to his sermons and rioted against the Medici's forcing them to flee for a short time. Condemning the sin of vanity by displaying artwork considered sinful countless masterpieces were piled in the plaza and burned in what he called "The bonfire of the vanities." He also burned people. After a while Alexander VI had enough of him and he was burned.
When Martin Luther posted his 95 theses, the last thing on his mind was defying the pope or breaking away from the church. The pope looked upon this attack on indulgences as a personal attack on his authority, which as the church taught was derived by God and the only the pope speaks for Jesus. Savonarola and Huss were prominent examples of how far Rome would go to preserve it's authority.