Under the reign of Henry VII. After taking the crown at Bosworth, Henry massively increased its wealth and power. In 1504 he banned nobles from maintaining private armies unless they had received a royal licence, which came with a price tag. The aristocracy had, however, been gradually moving away from the military side of things for centuries. It's important to note a distinction here. Lords were nobility and, in general, did not become the gentry. The gentry were the descendants of landed knights, successful merchants and the wealthiest free peasants. So while a civilian gentry had been developing for a long time by 1504, lords retaining private armies had recently been very common. Henry VII's actions didn't bring a complete end to private warfare; the sixteenth century was the golden age of the border reivers, but this was on a far smaller scale in comparison to the retinues raised by the fifteenth-century nobility.