The Eastern Roman Empire, also known as the Byzantine Empire, is something that doesn’t exactly loom large in the consciousness of the British public (unlike the Western Empire), but it did play a huge role in history and lasted over a thousand years.
But how did an Empire that once stretched from the Balkans deep into the Middle East, with enclaves in Italy and North Africa, fall?
There are several reasons. The rise of Islam is an obvious one (Islam swiftly rolled up the exhausted Persian Empire and the Ottoman Turks were the ones who finally conquered Byzantium [aka Constantinople]). Another is the Fourth Crusade, arguably the most stupid piece of foreign policy in the history of Western civilisation. The split between Catholic [ironically a term coined by the Eastern Emperor Theodosius, if memory serves] and Orthodox Christianity, which played a substantial role in the Fourth Crusade, is one more.
But perhaps the biggest reason wasn’t the military defeat at Manzikert, or religious bickering but a decision made by an emperor who was, in many ways, a very capable man with a golden opportunity to make huge headway that he missed.
After a run of mostly dreadful emperors, Alexius Comnenus put the Empire on a stable footing and played a logistical and diplomatic master stroke by enabling the First Crusade to be fed and watered without huge grievance (although there was some bitterness, especially later, as the Crusader states and Eastern Empire became less co-operative). His son, John Comnenus, was a great leader who helped reconquer territory from Turks who were, at this stage of history, on the back foot.
Manuel was the son of John, and faced a decision: East or West? It wasn’t wholly binary (the Empire couldn’t pretend either didn’t exist) but it was a question of focus.
Manual did campaign in the East, to good effect, but he also sent huge quantities of men and money west. After his rival, Roger, King of Sicily, died and his successor faced rebellion, Manuel sensed opportunity. With hindsight, it was, perhaps, a mistake.
Initial military triumph in Italy due to the disarray and rebellion there was coupled with diplomatic success with the papacy (the church having suffered a schism some time before this point). With reconquered territory in Italy (until the 8th century the Eastern Empire had ruled an exarchate in Italy) and alliance with the Pope, Manuel’s decision appeared vindicated.
But things went awry. One of his generals alienated the locals by his approach and was recalled. When, immediately prior to battle, mercenaries demanded a vast increase in pay and were refused, they defected. Defeat was suffered, and all the time, money and manpower spent yielded only a small presence in Italy.
The ultimate threat to the Eastern Empire was not Italy, nor the Pope. It was not even Venice and Genoa, though those cities would pick over the dying body of Constantinople as a proxy for their trade war. It was the Turks. Manuel could have and, in retrospect, probably should have focused his attentions strictly on the East. It was from here that his manpower was drawn, particularly Anatolia (modern day Turkey).
It may seem harsh to pick out Manuel. He was a good, competent man, personally brave and well-liked. But it is in the summer of prosperity that the seeds of ruin are sown. It was luxury that enervated the Western Empire, as Gibbon wrote. A wretch cannot hope to achieve success except by extraordinary luck, but a talented man has the potential to achieve a lot with wise decisions, and failure to do so can lead to future penalties that are not immediately obvious (Marcus Aurelius permitting his ‘son’ to become emperor being a prime example).
Manuel’s son (a child at accession) was overthrown, and his overthrower in turn deposed. This led to the end of the Comneni dynasty which had furnished three great and long-reigning emperors and ushered in the disastrous Angeli dynasty under whom the Fourth Crusade occurred, a blow from which the Empire never recovered. That was just over 20 years after Manuel’s death.