Unitarianism first developed as an institutional movement during the Protestant Reformation in Europe. Transylvania and Poland, the countries where Unitarianism initially appeared, were far from the power centers of both the Catholic Church and the Magisterial, or mainstream, Reformation. It was precisely because of the distance from the power centers of Christian orthodoxy that early European Unitarianism was able to thrive. The fate of the Polish and Transylvanian Unitarian movements rose and fell with the relationship of those countries to the Catholic Church and the Magisterial Reformation.
The case of the Unitarian movement in Poland is particularly instructive in this regard. In 1565, the Reformed Church of Poland, a Calvinist body, split over doctrinal issues. The orthodox members of the Reformed Church held to a trinitarian understanding, believing that God the Father, the Holy Spirit, and Jesus Christ were all part of one divine being. The liberal members rejected trinitarian theology, in favor of a variety of different understandings of who Jesus was. Some liberals believed Jesus was fully human and not divine at all. Others argued that he was divine in some way but not equal to God the Father. All of the liberals agreed that the traditional Trinitarian views promoted by the orthodox lacked scriptural basis, and defied reason.
Despite these theological disagreements, the Polish liberals appealed for church unity. They argued that there should be room within the Reformed Church for a variety of viewpoints. The orthodox disagreed, and refused to affiliate with the liberals.
Once separated from the orthodox, the liberals quickly organized their own body, which they called the Minor Reformed Church of Poland. The church tolerated a wider divergence of views than many other churches of its day. Views of Jesus, for instance, ranged from those held by the minister Simon Bundy, who regarded Jesus to be fully human and as such did not invoke his name during worship, to others who affirmed Jesus' divinity but did not place him as an equal to God.
Members of the Minor Reformed Church sought a middle path between the social teachings of radical Anabaptists, who urged non-compliance with secular authorities and absolute pacifism, and those who argued that Christians must obey their government. Under the guidance of Faustus Socinus, the church's major theologian, the Minor Reformed Church developed a code of behavior that encouraged participation in the government as long as it was not in conflict with the teachings of Jesus or the individual's own conscience.
The Minor Reformed Church flourished from 1565 until 1660, at which time the power of the Catholic Church in Poland was again on the rise. The liberal Reformed community was suppressed by the Polish government and its members exiled.
During its brief existence, the Minor Reformed Church emphasized that living a Christian life was more important than adhering to a specific set of beliefs. The Minor Reformed Church's greatest accomplishments lie in the realm of education and theology. The founding members established the community of Rakow, near the Polish city of Krakow, as the unofficial headquarters of the Minor Reformed Church. In Rakow, they built a college and installed a printing press. The college became a center for liberal thinkers from across Europe; at its peak, about a third of its 1,000-member student body came from outside Poland. The printing press began to publish and disseminate the radical religious ideas of the movement. The Racovian Catechism, a document which outlined the basic teachings of the Minor Reformed Church, was translated into Latin, Dutch, English, and German within only a few years of its publication. As a result, the Polish catechism had an impact on religious thinkers throughout Europe, and helped influence the development of Unitarian thought in England.