Christadelphianism began because of one man's idea that there was an "apostasy", long ago, that intentionally hid "the truth" for 1800 years, just waiting for him to re-discover it.
That's a borrowed idea, actually, because it's been around ever since the beginning of Christianity. If Paul, the self-proclaimed apostle, is to be believed then he disagreed with the "pillars" of the first church - especially Peter.
Yep, it's all in his letter to the Galatians and he made no bones about receiving his gospel from Jesus and God, so that he had no respect for the doctrines of the men he identified as Peter, James and John - he was right and they were wrong and Peter was to blame.
There was no apostasy, the churches merely evolved from this first contention and from then on the proto-orthodox was right and every other churches were heretical. Oh, and Paul did not win this early contention either. What won out, eventually, was a compromise between these two factions; the law-keepers and the salvation without works advocates. Not a willing compromise though, but one forced upon them by the Roman Emperor, Constantine.
If one insists on praying, pray that something so powerful as the Roman Catholic Church of the Dark Ages never happens again. Especially one like the Christadelphians who believe they are destined to rule the world "with a rod of iron" while everyone who disagrees with them will be "ashes under the soles of their feet".
No, John Thomas did not re-discover "the truth" after a bad boat ride. He mostly plagiarized his doctrines from John Epps, another wild-eyed insane preacher of that time, another quack quack doctor who believed in homeopathic remedies instead of real medicine. Robert Roberts, another quack who diagnosed diseases by feeling the bumps on people's heads, followed in John Thomas's footsteps and wrote "Christendom Astray", which has a whole chapter missing from the book because it was a chapter he wrote on prophecy - which failed miserably and became an embarrassment to Christadelphians.
When the new prophecy about Russia and Turkey fails (because Gog and Magog is misidentified as Russia by Christadelphians) will they be embarrassed? Probably not, because they weren't at all embarrassed by their 1988 prophecy failure. But, for those who would like to know, the ancient records of Assyria, discovered by modern archeology, identified Gog and Magog as Lydia and the Lydians in their day. Who are, as you might guess, no kin to the Russians at all.