Progress of thought was no easier in the West than in the East. The policy of authority in both quarters was suppression. In the eyes of the dominant Christian authority new thought was heterodox thought, and as such was wrong, because it implied thinking outside of the fixed limits. . . The term 'heresy' covers every kind of original thinking.[FOOTNOTE????]

Ecclesiastic response to heresy or to anything that could be construed as unorthodox was immediate and negative. By the time of the eighth century, if any new thinking was taking place, it was not being openly discussed nor widely disseminated, and it was not being written down. The period immediately preceding the controversy is not known for its magnificent literary or philosophical contributions.
The second important factor in the escalation of this conflict was the ongoing contest involving a struggle for political power between ecclesiastical and temporal authorities. In this context, a look at the difference in perspectives between Rome and Constantinople is enlightening. Pelikan explains that the eastern understanding of the relationship between church and state was different from that of the west:

The incumbent of the imperial throne in Byzantium was not thought to be, as was the incumbent of the imperial throne in the Western Empire, the recipient of an authority that was conferred by God through Christ on Peter and then transferred to his successors on the throne of Peter to the occupants of the new throne. Rather, the authority came directly from the throne of Christ to the throne of the emperor in New Rome.

This is a subtle distinction but an important one. The unique status of the Byzantine emperor was described metaphorically during the reign of Justinian as that of the new Melchizedek, the combination king and priest of the Old Testament. His authority derived, not from papal approval, but from Christ Himself.
Other factors which affected the controversy included the religious influences of Judaism, Islam, and the Monophysites as well as the wealth and influence of the monasteries, although scholars disagree about the influence of these factors on the motivation of both Leo III and Constantine V.
The Iconoclastic Controversy can be roughly divided into three periods: its emergence and development under Leo III and Constantine V, including the Iconoclastic Synod of 754, the regency of Irene and the Seventh Ecumenical Council of 787 (Nicaea II), and the revival of iconoclasm under Leo V, which lasted from 815 until the death of Theophilus in 842 and the subsequent regency of Theodora.
The official conflict started with Leo III, but the seeds of iconoclasm had been planted long before that time. Monophysite bishops were known to have condemned icons as early as the late fifth century, although Hussey notes that there is some evidence that the Monophysites did use icons. In the sixth century Gregory I chastised certain bishops who forbade icon veneration, stating that "pictures are the books of the illiterate, and you should not forbid them, while you should certainly forbid the worship of them." Tertullian had spoken out strongly against painted images in the second century, as had Clement of Alexandria. Icon veneration had been a controversial subject long before the reign of Leo III.
A great deal of speculation has been done as to why Leo III adopted an iconoclastic position in 726. Certainly his motives were at least partly religious. Leo had been exposed to both Jewish and Muslim culture, as well as Monophysite ideas, and none of these permitted the use of sacred images. Martin believes that Leo was engaged in an effort to purify Byzantine Christianity; when he assumed the throne, the morals of the people had deteriorated and superstition was rampant. Leo associated icon veneration with idolatry. According to Giakalis, support for his views may have come from an earthquake which occurred in 726, which Leo interpreted as evidence of divine wrath at the idolatry of the people. From a political perspective, Leo may well have viewed the continued military threats with which the empire was faced as a sign of God's favor toward those monotheists who insisted on a strict interpretation of the Old Testament prohibition against graven images. Peter Brown suggests that the cross was superior to the icon as a military symbol for the armies of Byzantium:

The emperors had to win in battle if they were to survive at all. For this purpose the sign of the cross, with its unbroken association with victory over four centuries, was a more ancient and compact symbol than any Christ-icon could be. When it came to winning battles, the cross was stronger medicine. . . By asserting that only a limited number of symbols were invested with the idea of the holy, the Iconoclasts were choosing just those symbols that best suited a more collective and highly centralized society.

However, Leo probably had other motives as well, political and economic motives which were later shared by Constantine V. Military and civil reforms were expensive, and the tax-exempt status of the church and its holding--including monasteries--reduced state revenues. In addition, the privileges of monastic life attracted men in large numbers, which meant that fewer men were available for field work and military service. Monasteries virtually controlled education, and their influence over the general population was considerable. They also possessed many sacred icons and relics, which attracted pilgrims from all over the empire. According to Sabev, "Monasteries were considered by iconoclastic emperors as obstacles to the implementation of their social reforms and the realization of their political ambitions." (It should be noted that not all scholars are in agreement about Leo's persecution of monasteries. Martin states that monasteries were not actively targeted until some thirty-five years after the beginning of the push for iconoclasm. Gero and Hussey both note that there is no certain evidence that Leo III persecuted monks during the 720s and 730s.
The first attempts of Leo III to impose iconoclasm on the people in 726 met with strong resistance. Public images were the first objects to be attacked. When Leo ordered the removal of a figure of Christ from the Bronze Gate of the imperial palace, the soldier who attempted to carry out the order was killed by a group of protestors, which Martin notes was made up largely of women. Several people were flogged, mutilated, exiled, or fined in connection with this incident, although none were executed. This would not be the last time that women responded with hostility and violence to imperial threats to sacred images.
Leo approached the patriarch of Constantinople, Germanus, several times in an ongoing effort to bring him around to acceptance of iconoclasm; Germanus was very old, very orthodox, and very stubborn, and he refused to yield. Meanwhile, the iconophiles, seeing the handwriting on the wall, were preparing their theological case, and John of Damascus, one of the chief defenders of the icons, issued his first statement in 727.
Although many of John Damascene's arguments were theologically complex, two of his best points were stunningly simple. He argued that the Jews were prohibited from making graven images for two reasons: first, their god was invisible and indescribable, and thus impossible to represent materially, and second, because of this first circumstance, the Jews were prone to idolatry. The followers of Christ, however, were in an entirely different situation. God was no longer immaterial, but had assumed human form, so that there was now a physical frame of reference for the creation of a likeness of his person, which in effect voided the prohibition against image-making. The physical, human form of Christ constituted permission to draw his likeness. John Damascene relied on scripture and on the unwritten traditions of the church in the development of his defense of the icons. He stated the theological support for icon veneration so skillfully that every subsequent writer used his arguments.
Leo III did not issue a formal statement against icon veneration until 730. He had been corresponding with Pope Gregory II, unsuccessfully trying to obtain papal support for iconoclasm. The letters grew increasingly hostile in tone; although they are mentioned casually by many historians without reference to their content, McGuckin describes one exchange which suggests that this was more than a friendly disagreement: "Leo threatens to come and smash the statue of St. Peter himself and imprison Gregory for his insolence and treachery, and the correspondence concludes with the Pope telling the Emperor not to trouble himself with the journey, as the Campagna marshes are at hand for his escape." Gregory could afford to be cocky; by this time, Byzantium had lost control of much of northern and central Italy. Leo responded to Gregory's obstinacy by seizing the Roman territory over which he still held control, including Sicily and southern Italy. It is apparent that issues of power and territorial politics were at least as much in evidence as theological matters.
It was at this time that Germanus was deposed by Leo, and replaced by Anastatius. Once again, angry women responded with outrage and attempted to stone the new patriarch to death; Anastatius was forced to hide in the imperial palace under Leo's protection until the crowd dispersed. As a result of this episode, Leo began to take stronger measures against icon veneration, and many iconophiles left Constantinople, where the persecution was the harshest. Nearly all of the church officials were replaced or converted to iconoclasm. For the last nine years of Leo's reign, few incidents are recorded, and it can be assumed that he felt he had accomplished his aim.
Constantine V, Leo's son, pursued a strong iconoclastic policy, and in fact it is his name which is most often associated with the controversy. Chroniclers of that period were all iconophiles, and they described Constantine in rather unsavory terms. Theophanes, for example, refers to him as a "totally destructive bloodsucking wild beast" and "the forerunner of the Antichrist." Many of the criticisms about his personal habits and supposedly bizarre religious practices are without historical foundation. Constantine V was an intelligent and skilled theologian, although his three marriages and alleged bisexuality would suggest that his moral standards were no more orthodox than his theological views. He was, however, an able ruler and a skilled military commander, and his troops contributed much of his success in this area to his iconoclasm.
Constantine V provided evidence of his future leanings at his baptism, performed by Germanus in 718. Theophanes provides this entertaining description of the event:

While Germanus the chief prelate was baptizing Leo's successor ( in both his evil and his rule) Constantine, the boy, because he was so young, gave a terrible foul- smelling harbinger: he defecated in the holy font, as say those who were accurate eyewitnesses. This made the Patriarch Germanus prophetically say, "This is a sign that in the future great evil shall befall the Christians and the church because of him."

Constantine did not take any iconoclastic action for the first ten years of his reign. There was little need; the hierarchy was by that time almost exclusively iconoclastic. When he called a council in 753 it was not opposed, and over 300 bishops were present. Peaceful propaganda had accomplished what force could not. Constantine had intended for this council, held at Hieria, to be ecumenical. (It was not.) Of the acts passed by this council, all that survives is the Definition, preserved in the Acta of Nicaea II. The council was in session for seven months. Constantine prepared many of the theological arguments supporting iconoclasm himself. The decision of the council anathematized icon veneration, and stipulated that to venerate, make, set up in a public place, or even own an icon--any painted religious representation or likeness--was a criminal act, and it stated further that monks guilty of this crime would be prosecuted as enemies of God and the state. One result of this, perhaps the primary intended result, was that Constantine was able to give free reign to the persecution of his real targets--the monasteries.
The resistance to the policies of the first Iconoclastic Council centered in the monasteries, and the theological arguments in defense of icons were all the work of monks. Opposition gathered around Stephen, the abbot of a monastery on Mount Auxentius. Stephen was arrested and tortured at least twice for his refusal to accept and obey the law, and the last fatal episode involved a severe flogging, after which he was dragged down the road and beaten to death. His body was defiled, and his corpse was thrown into a hole containing the bodies of pagans and criminals.
Over the next ten years persecution of the monasteries continued with increasing fury. Monks fled by the thousands to Italy and other parts of western Europe, taking with them much of the art, learning, and culture of the East. Their buildings and land holdings were appropriated by Constantine; some were turned into army barracks, while others were simply destroyed, along with their priceless contents: books, art work, relics, and many sacred objects. Constantine's reign of terror ended in 775.
His son and successor, Leo IV, abandoned many of his father's anti-monastic policies and appointed heads of monasteries as bishops and other officials. Leo supported iconoclasm, although not as rabidly as Constantine had, and when his wife Irene was found to be hiding images in her quarters Leo refused to live with her any longer. He died in 780, after a brief and unremarkable reign.
Irene was a devout iconophile. At the time of Leo IV's death, Constantine VI was a small child, and Irene ascended the throne as regent. Within a year of Leo's death, Irene had begun the process of restoring the icons. She waited patiently for three more years before writing to the pope and requesting an ecumenical council. The patriarch had died, and Irene appointed Tarasius to replace him.
The council opened in Constantinople in August of 786, but was disrupted almost immediately by iconoclast soldiers who were still loyal to Constantine V, and the council was forced to disband. Irene had these iconoclasts transferred, and she replaced them with others more sympathetic to her aims. It was decided that Constantinople was not the best place for the council to be held, since it was the site of the Iconoclastic Synod, and the new council was scheduled to be held in Nicaea in May of the following year.
The council finally assembled in September 787 in the Hagia Sophia. The Synod of 754 was officially anathematized. Icon veneration was restored, and anathema was pronounced on any who failed to venerate the holy icons. Iconoclastic bishops who had persecuted monks were deposed. Iconoclastic writings were to be collected and delivered to the office of Tarasius, patriarch of Constantinople, where they would be kept under lock and key; to retain any such documents would result in excommunication.
Later assessments of this council are interesting. Its ecumenicity was challenged a number of times by such noteworthies as Theodore Studites and Charles the Great. Pope Hadrian initially expressed doubts that the issue to be examined--iconoclasm--was serious enough that a council needed to be convened. He was not much interested in icons one way or the other; what was far more important to him was the return of valuable church property which had been confiscated by Constantine V after the Iconoclastic Synod, and it is likely that this was his principle reason for agreeing to Irene's request for a council. However, this issue was not even addressed. Hadrian viewed Nicaea II as a local council, since in his mind orthodoxy had never been in question, and the Roman church had not recognized the Synod of 754. Later statements by him indicated that he was not displeased with the East's formal return to orthodoxy; however, he was not at all happy that the question of church lands had not been raised by his representatives.
Iconoclastic elements were not entirely eliminated by the acts of Nicaea II, however. Irene's son, Constantine VI, had his own reservations about icon veneration. As he came into his majority, he grew impatient about Irene's reluctance to turn the throne over to him, and he was able to rally support from among the iconoclasts who were still on the scene. Irene was not a particularly able ruler militarily, and Constantine was able to successfully argue that it was her veneration of icons that accounted for a series of military disasters. The defeat of her armies was a sign of divine displeasure.
Irene was exiled, but she eventually returned to rule with Constantine VI for a time. Most historians state that she tired of sharing the throne and had him blinded so that she could rule alone. But she encountered little opposition from his former supporters. Constantine VI had committed a serious error in judgement when he divorced his wife, married his mistress, and placed her on the throne. The "so-called adultery or moechian controversy" may have removed him from the throne if Irene's act had not. Since the one certain way to replace an unpopular emperor was to kill him, Irene may have saved his life. (Theophanes believed that the purpose of the blinding was to kill him, but why blind a man if the intent is to kill him? ) In addition, although she has been harshly judged by historians for her decidedly unmaternal deed, it is possible that she felt strongly enough about icons that this seemed the only way to preserve the work of the Nicene Council.
Whatever her motive might have been for taking Constantine VI out of the picture, Irene's major achievement as Empress was the restoration of the icons. In other ways, her performance was less than outstanding. She did not remain long on the throne after the coronation of Charlemagne in 800, and was deposed in 802.