Twenty-Year Anarchy

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**Twenty Years' Crisis**
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The Twenty Years' Crisis was a period of intense internal instability in the Byzantine Empire, marked by the rapid succession of many emperors on the throne. This crisis lasted from the first deposition of Justinian II in 695 to Leo III's ascension to the throne in 717, beginning the Isaurian dynasty.

**Background**
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The Heraclian dynasty, which ruled the Byzantine Empire from 610, was destroyed during this period. The crisis was accompanied by the intervention of young foreign states that appeared after the Byzantine-Iranian War (602-628). This war, also known as the "World War of the VII century" by Lev Gumilev, led to the emergence of new powers in the region.

**Alliances and Interventions**
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The Western Turkic Khaganate, which was a major ally of Byzantium during this period, disintegrated into Bulgaria and the Khazar Khaganate in 658. These two states supported the return to power of Justinian II in 705 and Philippicus Bardanes in 711.

In 661, the Umayyad Caliphate was established, which consisted of former Byzantine and Iranian territories. The caliphate supported the coming to power of Leo III of Isaurus in 717.

**Currency Crisis**
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The conquest of Egypt by the Arabs in 639 led to the loss of the Byzantine gold mines in Bir Am Fawakhir. In 689, Justinian II reinstated a treaty with the Umayyad Caliphate, establishing joint sovereignty over Armenia and Georgia. The division of the kharaaj (tax) between the two powers was agreed upon.

For some time, both the Umayyad dinar and the solidus were in circulation in areas under joint administration, such as Cyprus. A dispute arose in 692 regarding the exchange rate between these currencies.

**Conclusion**
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The Twenty Years' Crisis marked a significant period of instability in the Byzantine Empire, leading to the downfall of the Heraclian dynasty and the rise of the Isaurian dynasty. The intervention of foreign powers and the emergence of new alliances contributed to this crisis, which had far-reaching consequences for the empire's internal politics and economy.