Beginning in the 16th century with the Protestant Reformation, however, individual movements began to splinter Christians away from the Roman Catholic Church to follow new interpretations of the Bible. Many of these teachers like Martin Luther and John Calvin professed a better understanding of Scripture—an understanding which condemned some of the practices of the present Christian Church, the Catholic Church.
Many of their points were truly great, as were many of their criticisms, but the resulting division of the Christian Church was devastating and lamented, strongly, by even Martin Luther himself.
Source: K. Albert Little - The Cordial Catholic on Patheos, 1 May 2015, "Dear Christians: Take Our Unity Seriously, Because Everyone is Watching", http://www.patheos.com/blogs/albertlittle/dear-christians-take-our-unity-seriously-because-everyone-is-watching/