Origin 325 to 451 CE
The claim is that the eternal Word became a specific first-century Jew without ceasing to be God. Christianity spent four centuries working out how to state that without saying something it considered fatal, and the working-out cost it its unity.
The council at Chalcedon in 451 produced the formula the Catholic, Orthodox and Reformation churches all inherit: one person in two natures, divine and human, without confusion, without change, without division, without separation. Each of those four negations rules out a position someone was holding.
Chalcedon did not command assent. A large body of churches, Coptic, Syriac, Armenian, Ethiopian, Malankara, rejected the formula and were labelled monophysite, a label they have always disputed. Their own term is miaphysite: one incarnate nature of the Word, in which divinity and humanity are united without mixture. The Church of the East, separately, was accused of dividing Christ into two persons, and it likewise disputes the charge.
The twentieth century largely settled that these were disputes about vocabulary rather than substance. Rome and the Oriental Orthodox churches issued agreed christological statements confessing a common faith in the incarnate Word, and a Common Christological Declaration was signed with the Assyrian Church of the East in 1994. The churches remain separate for reasons of jurisdiction and history. The heresies they were divided over have, in the judgement of their own hierarchies, turned out largely not to have been held by anyone.