The Christadelphian movement was founded in the USA by John Thomas (1805-71), with its earliest components being established around 1848. Thomas was a doctor who had been born in London but emigrated to the USA in 1832. Thomas was shipwrecked on his way to America, and while he was in danger he realised that he knew little about what would happen to him after death. He decided that if he survived he would devote himself to religious studies. He carried out this intention, though he did not believe that he had any special revelation from God and based his writing solely on the close study of the Bible.
In 1834 Thomas founded a magazine called The Apostolic Advocate, in which he published his developing ideas of true Christian belief. Throughout the 1840s he began to attract a following of people sympathetic to his developing views, and gradually congregations grew up. Thomas founded another magazine, The Herald of the Future Age, in 1844, and moved to Virginia. As well as working in the USA he made a number of successful speaking tours of the UK.
The group became a recognised movement and took their present name in 1864, partly as a result of the American Civil War. Their allegiance to Christ and the related objections to bearing arms in the service of a worldly state meant that members wanted to be conscientious objectors and refuse to fight. They could only do this if they were members of a recognised religious group that opposed the war, and so the Christadelphians came into being, with the name being derived from a Greek phrase, Christou adelphoi, which means 'brothers (and sisters) in Christ'.