Second coming of Jesus. Millennialism will be 1,000 years of peace on Earth. When is it going to happen? How is it going to happen? Pre-millennialism-1,000 years of peace on Earth will begin with Jesus' arrival. Post-millennialism-Jesus will come after 1,000 years of peace on Earth. Advocates for social reform. Millerites-William Miller-October 22, 1844-says that's when Millennialism will occur-became the Great Disappointment.