The "Great apostasy" idea is also crucial to Mormonism. (they also give a hat-tip to Martin Luther, as does the WT on occasion. )
Fragments of Jesus Christ’s Church were all that remained and doctrine was often mixed with pagan practices or the practices of other religions. The world fell into apostasy , which means that the truth of the gospel was not on the earth. There were no prophets to lead the people, and man was left to his own wisdom. This does not mean that God and Jesus Christ completely ignored mankind. There were times that men were guided to certain places or ideas. Members of the Mormon Church, for instance, believe that Christopher Columbus was led to the Americas by the Spirit and that the discovery of the Americas was instrumental in God’s plan for us. The new land provided a place where a new government could arise, a government that had built into its framework a tolerance for all religions. Mormons also believe many of the reformers of religion, such as Martin Luther, were inspired of God.
The restoration of the Jesus Christ’s Church came about through Joseph Smith (understandingmormonism.org)