Churches were merging into the Roman Catholic church in Constantine's time, and they are merging into the Roman Catholic church in our times, and they were merging into Roman Catholic likeness, also in the realm of church and state being married, and so it is today, and also in the realm of the Nicolaitans' doctrine, which was the clergy over the laity, and so it is today, in a much bigger way than we think.
These problems didn't happen overnight though....the Reformation never entirely got rid of the old leaven and now it is growing up like weeds and maturing into it's evil fruit. That is the lesson of ancient Israel that we should have learned from, who turned back to the Lord in a measure but didn't get rid of all her idolatrous high places. Power corrupts....and this is true in churches/ministries too....that's why we need to keep to the simplicity of Christ. Flesh is prone to the same in any sphere. God has been longsuffering, but now He has written "Ichabod" over many doors, His Spirit departed, and He is giving them over to captivity.