Monarchianism or Monarchism is a set of beliefs that emphasize God as being one person and the only ruler of his kingdom. The term "Monarchians" or "Monarchists" was given to Christians who defended the "monarchy" of God in a reaction against the Logos theology of Justin Martyr and the apologists, who had spoken of Jesus as a "second god".
Models of resolving the relationship between the God the Father and the God the Son were proposed in the 2nd century, but later rejected as heretical by the Christian Church when the doctrine of the Trinity was developed at the First Council of Constantinople, in which it was decided that God was one being that consisted of three persons: the Father, the Son, and the Holy Spirit. Some of the earliest Monarchians were called Alogi because they opposed the doctrine of the Logos, as explained in the canonical Gospel of John.
Monarchianism in-and-of itself is not a complete theory of the relation of the Father, the Son, and the Holy Spirit, but a simple tenet that requires further extension. There are basically two contradicting models of Monarchianism:
According to the Catholic Encyclopedia, Natalius was an early Patripassianite. He was an antipope (rival bishop of Rome) just before Antipope Hippolytus. According to Eusebius' EH5.28.8-12, quoting the Little Labyrinth of Hippolytus, after being "scourged all night by the holy angels", covered in ash, dressed in sackcloth, and "after some difficulty", he tearfully submitted to Pope Zephyrinus.
Another proponent of Monarchianism was Paul of Samosata, who however does not neatly fit in either of the two models.
Emanuel Swedenborg has also been seen as a proponent of Monarchianism, since he emphasizes a uni-personal God. However, he does not see God as appearing in three modes; rather, he sees God as one divine person, Jesus Christ, who has a divine soul of love, divine mind of truth, and divine body of energy. Jesus, through a process of uniting his human form to the divine, became entirely one with his divine soul from the Father to the point of having no distinction of personality.