The Great Disappointment was a result of the Millerite movement. William Miller was a self-ordained Baptist minister that proclaimed that the second coming of Jesus Christ would happen by 1844. His study of the Daniel 8 prophecy during the Second Great Awakening led him to conclude that Daniel’s “cleansing of the sanctuary” was cleansing the world from sin with the earth being the sanctuary in view. When Jesus did not return on October 22, 1844, this resulted in what’s known as the Great Disappointment.
It was out of this disappointment that the early Seventh-Day Adventist (known at that time as the Little Flock) movement was born and the doctrine of the Investigative Judgment began to take shape leading to the Seventh-Day Adventist Church incorporating in 1863.