The Reasons for the Decline of Christianity in Europe

What are the reasons for the decline of Christianity in Europe from 1675 until now?

While Christianity grew strong in Europe, especially during the Protestant Reformation, it slowly experienced a decline starting in the mid-to-late 1600s. This occurred for a number of reasons that accumulated over time. Today, Christians number in the low double digits or even high single digits in overall percentage in many countries in Europe. Do not count Europeans who came to America as a decline in the numbers of Christians in Europe. While it can be argued that the decline of Christianity began in the Middle Ages with the Catholic Church, please focus on the time after 1675.