In the first 10 chapters of Volume III, Gibbon addresses the rise and progress of other nations across Europe, Asia, and Africa during the second half of the first millenium. I will mostly skip the rise of the Bulgarians, Turks, and the fate of the Paulician heretics, as their stories are not that interesting to me in understanding the development of the Roman empire, particularly answering the central question of decline and fall the empire. The Turks will become important only with the rise of the Ottoman empire, which was eventually responsible for the fall of the Byzantine Empire. However, Islam arose as a powerful force and new superpower which came to effortlessly conquer large swathes of Asia and even Europe, including several crucial encounters with the Roman empire, so we shall not pass them over.

The Rise of Islam

Gibbon spends an entire chapter detailing the exciting life of Muhammad (570-632) as he rose from a random member of an Arabic tribe to a prophet and founder of a major world religion. We shall not fully recap the rise of Islam as it is not always directly relevant to the fate of the Roman Empire. However, while Muhammad himself did not live long enough to see Islam penetrate outside of Arabia, his successors, or caliphs, began a systematic expansionist effort which swept over Asia and parts of Europe over the next few centuries. The newly conquered territories were incorporated into the caliphate. At this point, Islam was still unified as a political entity, although even after Muhammad’s death there was already a great dispute over who his successor was to be: the supporters of Abu Bakr, one of his closest followers, clashed with those of his son-in-law Ali. Adherents to the former caliph came to become Sunni Muslims, while the latter became Shia Muslims, a distinction that continues to this way. While Ali managed to reign as caliph for a brief period, his sect became a minority, and most of the Islamic expansion was officially under Sunni caliphs.
Different generals were sent to Persia, Syria, Egypt, and Northern Africa to conquer territories in the name of Islam. The invasion force to Persia was led by the great general Caled (Khalid), also known as the Sword of God, who had already served with distinction under Muhammad. The Persian empire was already in decline and chaos after Heraclius’ daring expedition, and the approach of the Muslims was anticipated in great terror that the end had come for the empire. The entirety of the empire was rapidly overrun by the Muslim forces, including even their capital Ctesiphon. Their policy towards the conquered was simple, yet distinctive: they could choose to convert to Islam, pay tribute, or be killed. If one chose to convert to Islam, then their status was immediately raised from slave to brother. This extremely attractive arrangement persuaded many to join the ranks of Islam, accelerating the progress of the caliphate. In a short time, the centuries-old Sassanian Empire, which had resisted the efforts of all Roman emperors to conquer, was no more.
The Muslim army conquered Syria next, besieging and conquering the fortress of Bosra. They even convinced the Roman governor Romanus to convert to Islam. Emperor Heraclius was alarmed by these developments and raised an army of 70,000 under the command of general Werdan. They met the forces of Caled at the plains of Aiznadin (Ajnadayn) in 634. The Byzantines initially tried to bribe Caled’s army, who refused and proceeded to inflict an horrendous defeat on the imperial forces. Caled then proceeded to besiege Damascus, which fell after a dramatic siege of 70 days. Caled was ready to completely cleanse Damascus of any Christians, but they appealed to the more compassionate heart of fellow commander Abu Obeidah, who allowed the Christians to live as long as they paid an additional tax to the Islamic government, such that there is a Syrian Orthodox Christian population in Damascus even up to today. At the Battle of Yermouk (636), the Roman forces suffered an even larger defeat which marked the end of Roman rule in Syria. Syria came to be the seat of the dynasty of the Ommiyah (Umayyads) caliphate.
The progress of Islam in Egypt was similarly rapid. This was accomplished during the reign of caliph Omar (Umar), the successor of Abu Bakr. By this time, the Egyptians had grew tired under the oppressive taxation of Byzantine rule as well as the conflict over the nature of Christ, in which the mostly monophysite Egyptian church had been alienated from the Eastern Orthodox church. Thus the Christians were more than happy to submit to the Islamic conquerors under the command of Amrou (Amr). The rest of North Africa was eventually conquered during the time of the Ummayad Caliphate (661-750). During this time the caliphate also expanded to Europe, conquering the Iberian peninsula which was previously ruled by the Visigoths.
At this point, while I have chosen not to speak about Gibbon’s opinion of Islam, it’s interesting to quote his observations about the caliphate during this early period of Islam. The Muslims’ instant and full acceptance of anyone who converted to their religion is regarded as a remarkable thing: it became responsible for the caliphate’s ability to continually raise new armies filled with soldiers eager to become martyrs for their newfound faith. Gibbon also regards the simplicity of their beliefs and practices to be a stark contrast to the many levels of superstitions that had entered Christianity at this time:

More pure than the system of Zoroaster, more liberal than the law of Moses, the religion of Mahomet might seem less inconsistent with reason than the creed of mystery and superstition which, in the seventh century, disgraced the simplicity of the gospel.

Two Sieges of Constantinople

Constantinople was besieged twice by the Muslim armies. The first attempt was in 673/4, under the reign of the caliph Moawiyah. The siege lasted for six years. Here the Muslims underestimated the resources at the city’s disposal. Despite centuries of military decline, sufficient numbers of strong and disciplined soldiers were found for the defense of the capital, and the Byzantines’ possession of Greek fire, a new type of weapon based on flammable liquid which produced fire that could not be easily extinguished by water, was incredibly effective in repulsing the invaders from the walls. Thirty thousand Muslims fell in the failed siege, which momentarily restored Roman military reputation and forced a peace treaty between the two nations in favor of the Romans.
The second siege was attempted during the reign of caliph Sulayman in 717. Emperor Anastasius II made extensive preparations in Constantinople for the siege, but he himself would be killed, succeeded by the short-lived Theodosius III, and then the first of the Isaurian dynasty, Leo III, as we have already recapped in the last post. Leo III presided over the actual siege; he met an army of 120,000 soldiers under the brother of the caliph, Moslemah, and a navy of 1,800 ships from Egypt and Syria. Greek fire ships were launched against them and destroyed the navy. The caliph himself died of an indigestion shortly after the start of the siege, but the siege was still continued under his successor Omar. The first winter shocked the Arab and Persian troops who were used to warmer climates. In the spring, as they revved up their assault again, Greek fire came to the rescue of the Romans. Bulgarian troops, which had been paid into an alliance by Leo, played a major role in repelling the invading forces and killing 22,000 enemy troops. Moslemah was forced to withdraw, and thus ended Islamic attempts to take over the famed capital for the next few centuries.

The Victory of Charles Martel

 
The attempt to expand beyond Spain into Gaul was undertaken under the reign of caliph Hashem (Hisham, 724-743), who sent his commander Abdelrahmen. The first step was the siege of Arles in southern France, which was conquered smoothly. Aquitaine, on the other side of France which bordered the Atlantic, was also easily swept away by the Muslim forces. By this time,

The descendants of Clovis had lost the inheritance of his martial and ferocious spirit; and their misfortune or demerit has affixed the epithet of lazy to the last kings of the Merovingian race.
(Chapter LII)

The Merovingian kings were no longer de facto rulers; they only rubber-stamped the decisions made by the Mayor of the Palace, the real power behind the throne. In time, this position became a hereditary one by the time of the mayorship of Pippin the Elder. The mayor of the palace was styled as Duke and Prince of the Franks. Pippin’s illegitimate son, Charles, was the mayor when the forces of Abdelrahmen invaded, advancing all over Burgundy and planting their standards right outside of Tours in central France. The duke of Aquitaine, Eudes (Odo), was a rival of Charles who had ambitions for the Frankish throne and formed an objectionable alliance with a Moorish chief. According to Gibbon, Charles deliberately delayed his move to respond to the Islamic invasion to let them lay waste to Aquitaine, humbling any plans Eudes may have had. The duke was now reduced to imploring the assistance of his rival. The forces of the Franks met the Muslims at Tours (732), in a battle that would decide the fate of Europe for the next few centuries, perhaps even up to today.
The battle raged on for an entire week. For the first six days the Muslim forces held the upper hand, “but in the closer onset of the seventh day the Orientals were oppressed by the strength and stature of the Germans, who, with stout hearts and iron hands, asserted the civil and religious freedom of their posterity.” Abdelrahmen was slain, the Muslim army was completely routed, and Charles became savior of Christendom. The appellation of Martel (hammer) was added to his name. Eudes went on to reconquer Aquitaine, and the Muslim caliphate never again expanded beyond Spain.

The Liberation of Italy and the Rise of Charlemagne

The last time we spoke of the western provinces that Belisarius recovered during the reign of Justinian, the Lombards had invaded and occupied majority of Italy, but the empire was still in control of Rome and various valuable strips of land. The episode that precipitated the final loss of these holdings and the permanent end of the Roman empire in the west was the dispute over images that arose during the reign of the Iconoclasts, which we covered briefly in our breezing chronicle of six centuries of the Byzantine empire. The earliest Christian themselves were highly antithetical towards any statues, paintings, incense, or other forms of visual and sensual aids in their worship and churches, seeing their parallel with the idolatry of the pagans. However, after paganism had been destroyed, the parallel no longer remained, and as the number of Christians swelled as it was adopted as the official religion of the empire after the accession of Constantine, the clergy began to allow the return of images, seeing their benefit for the persuasion of the multitudes of the common people. Of course, the Enlightened Gibbon views this as part of the general comeback of superstition in religion – its expression was simply changed from pagan to Christian superstition.

But the superstitious mind was more easily reconciled to paint and to worship the angels, and, above all, the Son of God, under the human shape which, on earth, they have condescended to assume.
(Chapter XLXIX)

Several hundred years later, the rise of Islam, which completely prohibited any visual depictions of God, and the criticism of the Jews jolted a movement to restore the Church back to the purity of its beginnings. Emperor Leo III, perhaps through his exposure to Jews and Arabs, came to support this movement of Iconoclasts, decreeing the removal of images from the sanctuary and altar of the church. By this time, the eastern church under its Patriarch in Constantinople had roughly equal prominence as the Pope in Rome, but the former mostly acquiesced to the decree, as its proximity made it more amenable to imperial control. However, the western church saw this as an opportunity to assert their own independence. Pope Gregory II not only passionately defended the cause of the retaining of the images; he confidently asserted that the emperor, in interfering with the church, had stepped over the line and that as a the leader of the church on Earth he was fully in a position to chastise him. His forceful reply to the emperor inspired the Italians to rebel against the Byzantine exarchy in the west, violently massacring many Greek officials and supporters. Even Ravenna, the stronghold which had never been defeated, was not exempt: the forces of the supporters of the images prevailed over the iconoclasts and the exarch was killed. Leo sent a force to Ravenna to take back the city, but they were repelled by the Catholic forces. The Lombard king Liutprand, professing himself to be a champion of the images, was shortly accepted by the Pope as the new ruler of the Exarchy of Ravenna, freeing it from two hundred years of Byzantine control since the time of Justinian.
This was not for long, however, as Astolphus, Liutprand’s successor, oppressed the Romans; they turned to the court of Charles Martel, the savior of Christendom. Martel gave his son and heir Pepin to their cause, and Pepin completely defeated the Lombards. Boosted by his fame as the champion of Catholicism, Pepin was eventually crowned as the new king of the Franks with the blessing of the Church – he became the first of a line of Carolingian kings, and marking the end of the Merovingians, from which Clovis and Childeric had descended. The rule of the Carlovingians was distinguished in the close link between the crown and the church. The son of Pepin, Charlemagne, would effectively rule Rome: the Pope greeted him as an emperor, the people swore allegiance to him, and he was involved in examining and ratifying the election of popes. In return, the Carlovingians greatly supported the cause of the Church. One of the first actions was Pepin’s donation of the Exarchy of Ravenna to the Pope. For the first time ever, the Pope became administrative ruler of an actual region on Earth. Such donations of land and treasure would become commonplace over the next few generations of Carlovingian kings.
In 799, pope Leo III barely survived an attempted assassination by conspirators who favored the election of a nephew of the previous pope, Hadrian I. He fled to Charlemagne’s camp in Paderborn, Westphalia, and was sheltered there. When Leo was restored back to the seat of the Catholic throne, he expressed his gratitude by crowning Charlemagne as Emperor of the Romans. This effectively was an act of rebellion against the rule of Empress Irene in the East, where the Byzantines had always claimed to be the true successors of the Roman empire.
The rule of Charlemagne indeed marked a restoration of sorts of the Western empire. He conquered and ruled over an empire stretching across France, Spain, Italy, Germany, and Hungary. His rule came to be recognized even by the Byzantine empire: he addressed the ruler of the East as brother instead of father, and the Byzantines likewise addressed him as emperor of the Romans, although this appellation would be withdrawn from his less capable sons when they succeeded him. He concluded a treaty of peace and alliance between the Eastern and Western empires, where they recognized the territorial claims of both states.  Gibbon himself regards the greatness of Charlemagne as being overblown; according to him, Charlemagne’s merits were exaggerated by comparing him to the barbarian background from which he emerged. Gibbon also judges Charlemagne’s efforts to reform the Frankish legal system as not reflecting that of a true legislator, perhaps compared to the reforms of Justinian or Basil. Charlemagne was also illiterate throughout his life; our author looks down upon his relatively feeble attempts to educate himself. That being said, at the end of the day Gibbon gives Charlemagne some credit:

The dignity of his person, the length of his reign, the prosperity of his arms, the vigour of his government, and the reverence of distant nations distinguish him from the royal crowd; and Europe dates a new æra from his restoration of the Western empire.