Who, when, how did dispensationalism come out of the Reformed camp? This is what I read from Wikipedia:
John Nelson Darby (18 November 1800 – 29 April 1882) was an
Anglo-Irish Bible teacher, one of the influential figures among the original
Plymouth Brethren and the founder of the
Exclusive Brethren. He is considered to be the father of modern
Dispensationalism and
Futurism. Pre-tribulation rapture theology was popularized extensively in the 1830s by John Nelson Darby and the
Plymouth Brethren,
[1] and further popularized in the United States in the early 20th century by the wide circulation of the
Scofield Reference Bible.
[2]
Charles Haddon Spurgeon, Pastor of the
Metropolitan Tabernacle and contemporary of Darby, published criticism of Darby and Brethrenism.
[19] His main criticism was that Darby and the Plymouth Brethren rejected the vicarious purpose of Christ's obedience as well as
imputed righteousness. He viewed these of such importance and so central to the Gospel that it led him to this statement about the rest of their belief.
James Grant wrote: "With the deadly heresies entertained and taught by the Plymouth Brethren, in relation to some of the most momentous of all the doctrines of the Gospel, and to which I have adverted at some length, I feel assured that my readers will not be surprised at any other views, however unscriptural and pernicious they may be, which the Darbyites have embraced and zealously seek to propagate"
[20] -
Wikipedia page
The history behind the Plymouth Brethren, traces back to Ireland and originates from Anglicanism. Anglicans are a mixed bag, some are Calvinistic others are more Catholic.