Part of the reason for the wave of rebellion by "protest'ants or better known as Protestants was the fight fight against the kinds of sins, doctrines, practices, etc found within the Catholic church. It became more predominate with the spread of scripture in their own language. It became more predominate with people, who were willing, even under the threat of death, to preach the Word to the people.
The behavior of the Catholic Church to this rebellion, leaving, forming new congregations, was not Christ like. This was when scripture was used to point to the Catholic Church as befitting the title of harlot of Revelation, the AntiChrist, etc. Today, we again look to scripture to see who is befitting of the title in both name, behavior, and position of influence in this world.
So since this is the subject of study, let's set aside the finger pointing at this moment and start with the basics. What things identify who is this horrid creature? What characteristics stand out that make her unique? What clues do we have and what do they mean? Where on earth is she hiding? What is she doing? What is her influence on the kings of the earth? What is her goal?