Constantine IV in the context of "Scythia Minor"

The First Bulgarian Empire (Church Slavonic: блъгарьско цѣсарьствиѥ, romanized: blŭgarĭsko tsěsarǐstvije; Bulgarian: Първо българско царство) was a medieval state that existed in Southeastern Europe between the 7th and 11th centuries AD. It was founded in 680–681 after part of the Bulgars, led by Asparuh, moved south to the northeastern Balkans. There they secured Byzantine recognition of their right to settle south of the Danube by defeating – possibly with the help of local South Slavic tribes – the Byzantine army led by Constantine IV. During the 9th and 10th century, Bulgaria at the height of its power spread from the Danube Bend to the Black Sea and from the Dnieper River to the Adriatic Sea and became an important power in the region competing with the Byzantine Empire.

As the state solidified its position in the Balkans, it entered into a centuries-long interaction, sometimes friendly and sometimes hostile, with the Byzantine Empire. Bulgaria emerged as Byzantium's chief antagonist to its north, resulting in several wars. The two powers also enjoyed periods of peace and alliance, most notably during the Second Arab Siege of Constantinople, where the Bulgarian army broke the siege and destroyed the Arab army, thus preventing an Arab invasion of Southeastern Europe. Byzantium had a strong cultural influence on Bulgaria, which also led to the eventual adoption of Christianity in 864. After the disintegration of the Avar Khaganate, the country expanded its territory northwest to the Pannonian Plain. Later the Bulgarians confronted the advance of the Pechenegs and Cumans, and achieved a decisive victory over the Magyars, forcing them to establish themselves permanently in Pannonia.

The Typos of Constans (also called Type of Constans) was an edict issued by Eastern Roman emperor Constans II in 648 in an attempt to defuse the confusion and arguments over the Christological doctrine of Monotheletism. For over two centuries, there had been a bitter debate regarding the nature of Christ: the orthodox Chalcedonian position defined Christ as having two natures in one person, whereas Miaphysite opponents contended that Jesus Christ possessed but a single nature. At the time, the Byzantine Empire had been at near constant war for fifty years and had lost large territories. It was under great pressure to establish domestic unity. This was hampered by the large number of Byzantines who rejected the Council of Chalcedon in favour of Monophysitism.

The Typos attempted to dismiss the entire controversy, on pain of dire punishment. This extended to kidnapping the Pope from Rome to try him for high treason and mutilating one of the Typos's main opponents. Constans died in 668. Ten years later his son, Constantine IV, fresh from a triumph over his Arab enemies and with the predominantly Monophysitic provinces irredeemably lost, called the Third Council of Constantinople. It decided with an overwhelming majority to condemn Monophysitism, Monotheletism, the Typos of Constans and its major supporters. Constantine put his seal to the Council's decisions, and reunited such of Christendom as was not under Arab suzerainty.

Constantinople was besieged by the Arabs in 674–678, in what was the first culmination of the Umayyad Caliphate's expansionist strategy against the Byzantine Empire. Caliph Mu'awiya I, who had emerged in 661 as the ruler of the Muslim Arab empire following a civil war, renewed aggressive warfare against Byzantium after a lapse of some years and hoped to deliver a lethal blow by capturing the Byzantine capital of Constantinople.

As reported by the Byzantine chronicler Theophanes the Confessor, the Arab attack was methodical: in 672–673 Arab fleets secured bases along the coasts of Asia Minor and then installed a loose blockade around Constantinople. They used the peninsula of Cyzicus near the city as a base to spend the winter and returned every spring to launch attacks against the city's fortifications. Finally the Byzantines, under Emperor Constantine IV, destroyed the Arab navy using a new invention, the liquid incendiary substance known as Greek fire. The Byzantines also defeated the Arab land army in Asia Minor, forcing them to lift the siege. The Byzantine victory was of major importance for the survival of the Byzantine state, as the Arab threat receded for a time. A peace treaty was signed soon after, and following the outbreak of another Muslim civil war, the Byzantines even experienced a brief period of ascendancy over the Caliphate. The siege was arguably the first major Arab defeat in 50 years of expansion and temporarily stabilized the Byzantine Empire after decades of war and defeats.

Justinian II (Greek: Ἰουστινιανός, romanized: Ioustinianós; Latin: Iustinianus; 668/69 – 4 November 711), nicknamed "the Slit-Nosed" (Greek: ὁ Ῥινότμητος, romanized: ho Rhīnótmētos), was the last Byzantine emperor of the Heraclian dynasty, reigning from 685 to 695 and again from 705 to 711. Like his namesake, Justinian I, Justinian II was an ambitious and passionate ruler who was keen to restore the Roman Empire to its former glories. However, he responded brutally to any opposition to his will and lacked the finesse of his father, Constantine IV. Consequently, he generated enormous opposition to his reign, resulting in his deposition in 695 in a popular uprising. He only returned to the throne in 705 with the help of a Bulgarian army. His second reign was even more despotic than the first, and in 711 he was killed by mutinous soldiers.

Leontius (Greek: Λεόντιος, romanized: Leóntios; died c. 15 February 706) was Byzantine emperor under the regnal name Leo from 695 to 698. Little is known of his early life, other than that he was born in Isauria in Asia Minor. He was given the title of patrikios, and made strategos of the Anatolic Theme under Emperor Constantine IV. He led forces against the Umayyads during the early years of Justinian II's reign, securing victory and forcing the Umayyad caliph, Abd al-Malik ibn Marwan, to sue for peace.

In 692, Justinian declared war upon the Umayyads again, and sent Leontius to campaign against them. However, he was defeated decisively at the Battle of Sebastopolis, and imprisoned by Justinian for his failure. He was released in 695, and given the title of strategos of the Theme of Hellas in Southern Greece. After being released, he led a rebellion against Justinian, and seized power, becoming emperor in the same year.