The 670s were not an easy decade for the Eastern Roman Empire and its ruler, Constantine IV: the Umayyad Caliphate has overrun the Middle East and is pressuring Byzantium by land and by sea, besieging the Imperial Capital for 4 years (674-678), the Lombards are encroaching on the Italian domains, the Slavic tribes are on the move, besieging the great city of Thesaloniki (676-678), and, finally, in the north we have migrating Bulgars settling the lower Danube region.
IOTL, Constantine won 2 out of 3 of those battles, defeating Arabs and Slavs (and settling with the Lombards), but lost to Khan Asparukh at Ongal in 680, which led to the formation of the First Bulgarian Empire, to which Constantinople would have to pay annual tribute. And yet Constantine would live 5 more years, going on to purge his brothers Tiberius and Heraclius to deny them the throne, and dying at the age of 33, succeeded by a son so despotic and incompetent, he had to be overthrown twice.
But let's say Constantine fails to keep the Empire together. Say, he dies during the siege of Constantinople, the Empire falls to civil war between Heraclius and Tiberius, Constantinople falls to the Arabs (and with time, so does Asia Minor and the Aegean, if the post-Roman warlords don't watch out), Thesaloniki is sacked by the Slavs, and Khan Asparukh's New Bulgaria reaches as far as Thrace and the Aegean, perhaps helped by fleeing Byzantine officers who prefer him to the Arabs or can't make it as warlords.
What happens then, if the Second Rome falls, a mere 200 years after the first Empire, rather than a thousand years?
IOTL, Constantine won 2 out of 3 of those battles, defeating Arabs and Slavs (and settling with the Lombards), but lost to Khan Asparukh at Ongal in 680, which led to the formation of the First Bulgarian Empire, to which Constantinople would have to pay annual tribute. And yet Constantine would live 5 more years, going on to purge his brothers Tiberius and Heraclius to deny them the throne, and dying at the age of 33, succeeded by a son so despotic and incompetent, he had to be overthrown twice.
But let's say Constantine fails to keep the Empire together. Say, he dies during the siege of Constantinople, the Empire falls to civil war between Heraclius and Tiberius, Constantinople falls to the Arabs (and with time, so does Asia Minor and the Aegean, if the post-Roman warlords don't watch out), Thesaloniki is sacked by the Slavs, and Khan Asparukh's New Bulgaria reaches as far as Thrace and the Aegean, perhaps helped by fleeing Byzantine officers who prefer him to the Arabs or can't make it as warlords.
What happens then, if the Second Rome falls, a mere 200 years after the first Empire, rather than a thousand years?