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In 540, after Belisarius had besieged Ravenna, the Goths offered to make him Emperor of the West if he would rule them. He pretended to accept, used the offer to enter the city without a battle, and then handed Italy to Justinian. Justinian answered this proof of loyalty with recall, suspicion and withheld resources rather than reward, the pattern that runs through the novel to Belisarius's disgrace.
A ruler without legitimate military standing cannot read a subordinate's loyalty as loyalty, because the victories that prove the subordinate's worth also build the popularity that could topple the ruler. So each success raises the perceived threat, and the ruler starves, recalls or humiliates his most faithful servant while tolerating incompetent or corrupt generals who pose no danger.
The Blues and Greens began as chariot-racing fan clubs but worked as organized political blocs with patrons, street militias and theological loyalties. Emperors bought or courted their support. The Nika riot of 532 showed that a sporting identity could be turned almost overnight into an insurrection that nearly overthrew the throne, until Belisarius massacred the crowd in the Hippodrome.