What were the Protestants protesting and when did they start?
There have always been a group that differed from the Catholic Church. So to answer your question. Always. They didn't have the power or historians to publicize there was anything else until Martin Luther made a very public display that couldn't be ignored by history. Jesus and the disciples weren't RCC. They were Jews and practiced that religion on a heightened scale. There have always been a remnant church through the ages out of the limelight that kept the true religion that Christ taught including the observance of the 7th day Sabbath. What were they protesting? Power. The power of the priests. The fact that they kept Gods Word from the common people. Under pretense they said the people couldn't comprehend without "assistance".
I’m sure you understand what the word “protest” means. Most associate names like John Wycliffe, John Huss, Martin Luther, Tyndale, John Knox, with it. You know this, I’m sure, so what are you getting at?