He had formerly sworn allegiance to the king.
Jade, in spite of only possessing farmers, was able to raise them up. Because of his talent with tactics in this regard he was allowed the position of warlord.
Thanks to Jade becoming a warlord, the family is no longer hungry; a wealthy life was possible.
There was one important factor.
The king expected this position to be repaid with Jade's younger sisters when called upon, it was that kind of obligation.