Justinian's successor was his nephew Justin II, who ruled from 565-574, becoming progressively insane. He started his reign by refusing subsidies to the Avars. This was Turco-Mongol tribal confederacy (khanate), which swept from southern Russia to Bohemia and the Balkans. Westward expansion had been stopped in Thuringia by Meorvingian Sigibert, but they then moved to the Hungarian plains, destroying the Eastern Roman-allied Gepids by 564-6. When the Lombards went west in 565, they settled farther south in Hungary, using it as a base to organize raids with Slavs to Byzantine areas. Emperors had bought them off, but Justin II refused. The Avar reaction was a decisive thrust into Dalmatia, where they destroyed or plundered all in their path. In 571, Justin sought a truce, whereby he paid 80,000 pieces of silver, much more than the original subsidy. This Avar threat emerged during the same years as the Lombard descent upon Italy, so Byzantine forces could do nothing to stop it. Also in 571, Christian Armenia had rebelled against Sassanian rule, and requested Byzantine protection as a Christian power. Justin agreed, even stopping tribute payments to Shah Chrosroes. War ensued in the East. Persians took the important bishopric of Dara on the Tigris with more than 250,000 captives. Justin went rapidly insane, openly persecuting Monophysites. His wife Sophia was able to buy a year's cease-fire in the East, and got her husband to raise the Palace Guard general Tiberius as her co-regent.
Tiberius became Emperor in 578. The situation was dire. In 575-7, Turks had appeared for the first time as Byzantine enemies, taking a fortress in the Crimea. More pressing were the Avars and their Slav raiders. Though Tiberius tried to hold them back with payments, from 577, they had begun to infiltrate in large numbers into Thrace and Illyricum, actually over bridges that Greek engineers had built as part of the subsidies. In 580, the Avars laid siege to Sirmium on the Sava river near Belgrade, which fell in 582. In that same year a Cappadocian officer named Maurice succeeded to the throne when Tiberius died of poison. He tried to follow the policy of his predecessors--paying off the Avars and fighting the Persians. The Avars continued to raid, occupying more of the Upper Balkans. Money to fight in the East was also lacking.
Byzantium was blessed temporarily in 590. When Chosroes of Persia died in 579, he was succeeded by the shah Hormisdas. A coup took his life eleven years later, and his son Chosroes II fled to Greek territory. Maurice granted his request for aid, which Chosroes used to gain power. The latter had promised Maurice a peace treaty along with restoration to Byzantium of Armenia and eastern Mesopotamia. Miraculously, Chosroes II kept his promise until 603, when Maurice was deposed. For the remainder of his rule, the Emperor focused on three issues. 1) He organized what was left of Justinian's acquisitions. In North Africa at Carthage, and Italy at Ravenna, he established exarchates as Imperial command posts. Totally military in nature, an exarch ruled them with absolute control over both military and civil matters. This was a new consolidation of power, and was effective as long as forces were available. 2) From the 590s on the Emperor sent repeated expeditions against the Avars in the Danube region and beyond. None were decisive given lack of troop discipline. 3) Maurice tried to be as frugal as possible. He reduced military rations, and declined to ransom prisoners of the Avars. This ultimately led to his downfall; when he ordered the army to stay in the Balkans for the winter, they mutinied, and in the tangle of imperial aspirants, a certain general Phocas became ruler, massacring Maurice's family.
Phocas' rule was a disaster. Several senators, provincial governors, and generals did not recognize him; "his eight-year reign brought the Empire to the nadir of its fortunes." It began with Chosroes II invading Byzantine lands as Maurice's avenger. By 607 they had taken western Mesopotamia, Syria, Armenia as well as central Asia Minor. By 608 they had streamed as far west as Chalcedon, within sight of Constantinople. During the same years, Avar-Slav incursions increased, with few troops available to stop them. Phocas' response was a campaign to forcibly convert the Empire's Jews. Many of them lived in areas threatened by Persians; their natural response was to welcome Persian conquest. In Antioch persecuted Jews went to so far as to turn on the Christians, massacring them, triggering a total flight from the city. Soon, Blues and Greens rampaged in the capital.
Byzantium was saved from Phocas by the military governor system Maurice had established. The exarch of Carthage and his second-in-command brother were too old to claim power, but they prepared an army and fleet under their sons. The army proceeded to capture Alexandria in 609, moving on towards the capital. The fleet under Heraclius went to Thessaloniki, where it augmented its numbers, leaving for Constantinople in 610. On 5 October, Heraclius was welcomed as emperor by a population disgusted with the past decade of turmoil.
Heraclius is early Byzantium's tragic hero, and his reign can be divided into two parts, the first lasting until 628. He was occupied incessantly with the Persians and Avars. Until 620, the situation appeared hopeless. The Avars were disbursed throughout the Balkans, where their Slav partners began to remain during the winters. From the East, the Persians made repeated advances. The Persian general Shahr-Baraz took Antioch and Damascus in 613, moving to Jerusalem by 614, plundering it, destroying the Church of the Holy Sepulchre, and carrying off the True Cross. Having Occupied Armenia already, in 619, Persians extended as far as Egypt, cutting off food supplies to Constantinople, causing famine and disease in Byzantium, which was now reduced to the capital and small parts of Asia Minor and the lower Balkans. By 620, Heraclius was preparing to flee to Carthage, when the Patriarch Sergius implored him to stay, telling him that the entire people would support him, and the Church would open its coffers to him. In the next two years, Heraclius reorganized Western Anatolia. Divided into four Themes, each region was provided with a strategos, an all-powerful military ruler on the exarch model. In these themes, army-age males were settled on inalienable grants of land held in return for military service. These Theme Armies were further provisioned by taxation, forced loans, and church contributions.