"How are those people selected?"

By the power of money.

"What gives them their authority?"

The power of money.


The same was basically true in ancient Rome too, since wars could not be fought nor power successfully maintained without a ready and adequate supply of money to fund it.

On some occasions, of course, no amount of money could prevent a disaster occurring, as happened to Crassus...the richest man in the world at the time. He recklessly led a Roman army far into Parthia, got attacked by a huge force of Parthian horse archers and heavy cavalry. They first wiped out the relatively small contingent of Roman cavalry in a surprise attack. They then decimated he Roman foot soldiers by showering them with arrows, while the Roman formations were unable to counterattack effectively on foot against the swift Parthian cavalry. Crassus ordered his men to form "the turtle", a formation of interlocking shields which protected infantry from arrows. This rendered the formations unable to protect themselves properly from direct assaults by the Parthian heavy cavalry. The Roman force was annihilated, and Crassus was captured. Since he was famous for being the richest man in the world, the Parthians decided to dispatch him by pouring molten gold down his throat...a very nasty death!

Sometimes money just isn't enough.