After Constantine's 775 death, the Empire witnessed more than twenty-five years of instability. Leo IV died after five years in power, and was followed by the child Emperor Constantine VI (r. 780-797), whose mother Irene reigned and ruled as regent. An iconodule, she held a further church council in 787 that cast iconoclasm as heretical. Fearing for her position, she forced her son into the shadows and her husband's brothers into monasteries. As a result, iconoclasts focused their hope and support on Constantine, who was never able to challenge his mother effectively. She had him blinded in 797, and ruled independently until 802. To shore up support for herself in the weak position of a female ruler, she granted excessive tax exemptions to aristocrats, depleting the state's bullion supplies. Her proposal to Charlemagne of a marriage and reunification of the Empire, however, pushed her out of the pale of accepted conduct for Byzantine elites, who considered the Franks unreconstructed Barbarians. She was overthrown in 802, and Nicephorus I assumed the throne.
The Bulgar threat dominated Nicephorus I's reign (802-811). They had occupied Avar lands after the latter were defeated by Charlemagne, and threatened Constantinople with siege on a yearly basis. The Emperor fought them his entire reign, going so far as to destroy Khan Krum's capital at Pliska in 811, immediately after which the Byzantine leader was caught by the Bulgars in battle and killed with his forces.
After the short reign of Michael I, who was eventually deposed by a divided army, Leo V (r. 813-820) came to the throne. He was an iconoclast, but spent until 815 dealing with Khan Krum of the Bulgars. In 813-14, the Bulgars devastated Mesembria. After a parley with the Emperor at which Byzantine agents tried to murder Krum, the Khan laid waste to Adrianopole. In retaliation, the Emperor led an expedition deep into Bulgar territory, massacring the enemy, again at Mesembria. Krum then resolved to ruin the capital, but could not break through the walls. Overcome with frustration, he suffered a seizure, and died in 814. This ended the immediate Bulgar threat to Constantinople; Krum's son, Omurtag, made peace with Byzantium. Suddenly freed from the Bulgars, Leo tried to revive iconoclasm in 815, incurring iconodule ire. He was murdered in Hagia Spohia on Christmas Day, 820.
Michael II (r. 820-929) had been one of his assassins. A moderate iconoclast, he felt it best to just forbid discussion of the topic. During his reign, a renegade general named Thomas raised an army of Greeks, Armenians, and even Arabs, and received sanctuary on the Abbasid side of the border. Claiming to be the living Constantine VI, he marched to the Aegean, and was able to cross due to iconodule support. Michael was too weak politically to drive him away, and in 821 the capital faced a new siege from Thomas' forces for fifteen months. Finally, the Emperor invited the Bulgars to the outskirts of the capital to plunder and drive away the attackers. Also noteworthy during this period, the Arabs wrested Sicily and Crete from Greek control, turning them into raiding bases from which Latin and Greek possessions were then attacked for the remainder of the century.
Michael's son, Theophilus (r. 829-842), was well educated and interested in Arab culture and Islamic science. His major preoccupation, though, was fighting Arab advances. He only fought a rear-guard action in Sicily, judging Asia Minor to be of greater importance. By the time of his death, the Arab advances in Asia Minor had been kept to the occupation of a few forts. At the same time, iconoclasm had been restricted to little more than a clerical dispute. Theophilus' son, Michael III, was only three years old at his accession in 842; his mother Theodora ruled as regent. From 843 she permitted icons. Two years later, Abbasid power began to crumble, first with governorates breaking away, then with the central government's power decreasing within the Islamic heartland. In 856, Michael III came of age and overthrew his mother. A poor governor himself, he was surrounded with talented and influential advisers, such as Bardas. They founded a university in the capital, and his generals were able to defeat the Arabs in Asia Minor in 863, allowing Byzantium to pursue an offensive for the first time. The Byzantine Empire had outlasted two Islamic states as well as the iconoclasm controversy, and the Bulgars had not taken the capital. In 864, the Emperor was able to conclude an agreement with the Bulgar Khan Boris to defend the region against the Russians. Finally, Byzantine culture and civilization had even begun to expand to the north.
The most important question of this period regards the motivations behind iconoclasm. Much of this question involves the personality of its inaugurator, Leo the Isaurian. A military man from the east, he was intimately familiar with Islamic culture. Islam itself unequivocally outlawed any visual representations of humans in art, and was even clearer in its prohibition of visual representation of holy personages, in the general context of its excoriation of idolatry. Judaism, with which Leo was also familiar, had similar views, and it is possible that a Jewish physician in the court stoked his anti-icon feelings. As well, Leo may have been inspired by Islam, and wanted to cleanse the Eastern Church. After all, one could reason--and some did--that the Greek Church's straying from the path of total monotheism by permitting the use of icons had displeased God to the point of sending the Muslims as a punishment. Beyond that, it is true that illiterate Byzantine subjects unschooled in the finer aspects of theology often prayed to icons for their intercession with God or Jesus. Thus, several totally conscientious clerics did in fact support iconoclasm. Another possible motive for iconoclastic emperors, supported by leftist interpreters, has to do with land possession. A pervasive problem for post-700 emperors was bringing sufficient Anatolian land back into cultivation so that it would support Theme armies and provide tax revenue to the state. It was just such land, however, which was in the possession of monasteries immune to state exactions. From an Imperial administrative and military perspective, it was essential to strip monasteries of these lands and restore them to the Themes. That monks were as a whole iconodule can explain state policies here. There is little concrete proof of this motive, but the land need was there, and Charles Martel's similar and contemporaneous policies in the West are quite suggestive.