Why do jehovahs witnesses think the satin came to earth in the early 1900s?

Jehovah's Witnesses believe that Satan was cast down to Earth in the early 1900s as part of their interpretation of biblical prophecy, particularly drawing from Revelation 12:7-12. They associate this event with the establishment of God's Kingdom in heaven in 1914, which they view as a pivotal year marking the beginning of the "last days" or end times. This belief is tied to their understanding of the signs of the times and the increase of global turmoil and moral decline they interpret as evidence of Satan's influence on Earth.