Politics were organized differently than they are today. Back then, there were no real governments with standing armies. I mean, that had been the Roman ideal: that there would be a durable state supporting a standing army instead of it all being big shots with followers fighting each other.
Even the Romans, in their Imperial period, which the Byzantines continued, never really got out of the parochial tyrannous criminality of the Great Families, who were, first and foremost, looking out for themselves and their people. In most circumstances, everything political was expressed in military terms.
Big shots got bigger by making deals with smaller shots to supply military and material service up the line, all the way to the emperor or, on the other side, the Sultan.
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