Unitarianism was a significant minor strand of the radical Reformation in 16th-century Switzerland, Transylvania and Poland. Prominent among its doctrines were denial of the Trinity, affirmation of the divinity of Christ and divine biblical inspiration, adult baptism, and religious toleration.

In 1567, the Unitarian king of Transylvania, John Sigismund, proclaimed Europe’s first edict of toleration in over a thousand years. Our faith’s most prominent martyr was Michael Servetus, a physician who first described the pulmonary, or lesser, circulation of the blood. A century later, Unitarianism turned up in England, where it influenced John Locke and Isaac Newton, and then in British North America, where it touched Thomas Jefferson through his friendship with the Reverend Joseph Priestly, the discoverer of Oxygen.

Barely a decade earlier, Universalism had come to America from England, where the old doctrine that all human beings would eventually be saved through Jesus Christ and join in harmony with God in heaven had finally become the central doctrine of a separate denomination.

Much more evangelical than Unitarianism, which had a pronounced intellectual and urban ethos, Universalism spread across rural and small-town North America during the 19th and 20th centuries. Through their common emphasis on social action (such as the anti-slavery movement and the later suffragette and birth-control debates) and their evolving theologies of respect for the revelations of secular science, Unitarianism and Universalism drifted closer together, until their eventual official merger in 1961.

Thanks to Don Bailey for this summary of the history of Unitarian Universalism. For more detailed information, please read Unitarian Universalist Origins, Our Historic Faith by Mark W. Harris.