In AD 449, under the authority of Emperor Theodosius II, the Council of Chalcedon had convened and ultimately regarded Pope Leo I’s definition of Christ as possessing two simultaneous natures, both human and divine, to be orthodoxy. This was later known as the Chalcedonian Definition by historians and scholars. Despite the decision of the Council, however, sects existed within the Christian world that still did not accept the idea of two natures existing in one body. Apart from Nestorianism, the belief that the Incarnation of Christ existed effectively as two separate bodies with exclusive natures, there were also groups identified as Monophysites, those that believed that Christ existed with only one will or nature, these groups having segregated themselves after the rejection of Eutychianism that branded Eutyches a heretic in AD 448. Despite being reinstated in 449, he and Monophysitism came under scrutiny again at the Council of Chalcedon after the establishment of the Chalcedonian Definition.
Over 100 years later, following the Three Chapters, a series of writings that opposed Cyril’s Twelve Anathemas that asserted the Chalcedonian Definition as well as Cyrillianism as a whole, Emperior Justinian issued an edict that condemned these writings and reinforced the opposition to Nestorianism. A lesser objective of this tactic was also an attempt to reconcile with Monophysites and bring them back into the fold of the Orthodox Church. These were brought to bear on his authority at the Second Council of Constantinople in AD 553.
While the council was meant to have Pope Vigillus, a resident of Constantinople at the time due to conflict in the West with the Visigoths, Vigillus refused, finding his priorities to be more focused toward trying to sway Justinian to send military aid rather than address the Three Chapters. Vigillus was personally excommunicated and imprisoned within Constantinople, through the entirety of the Second Council, before agreeing to condemn the Three Chapters in December of 553.
During the Council itself, the Three Chapters were condemned without the Pope presiding over the proceedings. The canons that were to follow outlined the Chalcedonian Definition in finer detail: that the two natures it once alluded to were now two sets of exclusive attributes maintained in one person.
The initial response was not felt until the Pope, in his captivity, acquiesced to agree to their condemnation. This sent shockwaves through the Western portions of the empire. As a result, several bishops in Italy broke communion with Rome, arguing strongly against the Pope’s condemnation of the Three Chapters and affirmation of the new Chalcedonian interpretation. This would be known as the Schism of the Three Chapters. These grievances would not be rectified in their entirety until the end of the 7th century, when Aquileia finally accepted the condemnation, although far from willingly.
Before the end of the Schism’s effects, Monophysites had developed compromises to their beliefs in the forms of monoenergism (the belief that Christ existed with two natures, but one “energy”) and monotheletism (the belief that Christ existed with two natures but one divine will). These compromises were not sufficient enough to reunited them with Orthodox Christianity that believed in two distinct natures and wills respectively. The schisms that remained between Monophysites and non-Monophysites would only expand further between the conquests of Muslims as well as the Third Council of Constantinople.