The doctrinal structures of both Mormons and Jehovah's Witnesses are based on the premise that "real" Christianity died out after the first 2 to 3 centuries. Without this pretext, neither organization could doctrinally exist. The official assertion for both organizations goes something like this:

"True" Christianity died out sometime between the first century and the time Roman emperor Constantine took power. Both organizations claim that it was not restored until 1500 years later by Charles Taze Russell (for the Jehovah's Witnesses) or Joseph Smith (for the Mormons). Both groups point to the atrocities committed by the Catholic Hierarchy down through the dark ages as proof. 

 

This narrative ignores the objects of Papal hatred as well as the historical record of non-conformity of several groups of Christians. These groups, called by different names were never part of the Roman Church. In actuality, there were many tens of millions of Christians, spanning nearly one thousand years who refused to conform to the Sacerdotalism of the Roman Catholic Church. Many paid the ultimate price for this belief as this video shows.     

These dissenters and non-conformist groups are WITHOUT PARALLEL in all of world history in their record of faith while being subjected unspeakable tortures. These groups were aligned with politically connected Reformers in the 16th century for a brief period. The point is that MANY groups in the past and present have been neither Roman Catholic nor Protestant, just Christian.

Neither the Watchtower Governing Body nor the Mormon Priesthood wants this record of faith in Christ alone to be told because it undermines their mediator-like governance. 

The doctrine of a defeated church is falsified by the voices of millions of martyred believers as well as the Lord Jesus Christ himself when he said, 

... "and, lo, I am with you alway, even unto the end of the world." Mt. 28: 20b 

Alway: (Strong's) "inclusive of the parts of both extremes ; a period"

 

In other words, groups of bible-believing Christians have never disappeared from earth, as the Watchtower and the Mormon priesthood maintain.