The Battle at Thermopylae, or the 300 as it appeared in recent cinema media, is often touted as how the west defended itself, or Hellenic culture from the onslaught of eastern barbarism. Yet soon after Thermopylae during the Pellopennesian War the Spartans kept their alliance against the Athenians alive with Persian money. It makes political sense, the two naval powers in the Middle East at the time were Athens and Persia.
Alexander's expansion from Macedon into Persia shows a similar pattern of ethnogenesis. (more)
It has only really been with liberal democracy that executive and martial power has been disentangled. During the reign of Darius and the establishment of the Persian Empire, the provincial tax collectors, or satraps as they were called, were given full military power. This mimics the imperium granted to pro-consuls and pro-praetors who acted as provincial governors and tax administrators (not tax collectors) for the Roman provinces in the middle and late republic.
Prior to Muhammad, Arabia in the sixth century were dominated by tribes held together by either blood bonds, or a strong tribal leader. Islamic monotheism was the technology which enabled the higher level of social organisation amongst the Arabs necessary to conquer and control the Arabian Gulf. After Mumammad's death, Abu Bakr put down any insurrections to his caliphate but faced a problem. He had a military-agrarian complex. For socio-economic stability he chose to keep his army intact; expanding the Islamic Empire into Syria and Iraq by conquest.
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