A Reformation Blunder.
The "Protestant Reformation" of the 16th century initiated by Martin Luther produced some good fruits including greater Bible knowledge by the "laity"...the understanding that salvation is by by grace...encouraging individual relationship with God. But at what cost have these claimed gains been made?
Martin Luther started the "Lutheran" churches" which started the segregation ball rolling and it has been rolling ever since. John Calvin could not come to agreement with some of Luther’s ideas therefore, began to form his own churches (the "Reformed" churches).
The floodgates were now open wide, numerous other reformation movements surfaced, such as that initiated by John Knox (starting the Presbyterian church in 1560), Robert Browne (starting the Congregational church in 1592), and John Smyth (starting the Baptist church in 1609), none of which could come to agreement on the other's doctrines. Protestant denominations have catapulted ever since, causing segregation and disunity of the Body of Christ, causing literally thousands of denominational splits due to man-made doctrines and the lure of hierarchal authority and control that initiated the reformation.
This challenging quite comes from James Payton Jr’s book Getting The Reformation Wrong pg 257:
"Even so, the multitudes of church splits which have ensued in Protestant ranks – beginning already in the 16th century, increasing in frequency subsequently and achieving breakneck pace by the early twenty first century – have unquestionably managed to undermine the integrity of the gospel. The converse of what Jesus Christ prayed for (John 17) has come to pass: our lack of unity has rendered the gospel less credible in the eyes of the world. In this regard, we have sown the wind and have reaped the whirl wind."
The support of the segregation of the Body of Christ, for which He prayed for unity, is a great blunder of the Reformation.