He improved their training and equipment, but he also subverted their loyalties and turned them from a police force into a criminal gang who handed over the capitol on a moment’s notice.
Daemon didn’t war with the Stepstones because of trade, he did it because he wanted to be a king and likes fighting. Dorne would be on the hitlist, but so would Myr, Tyrosh, Lys, Pentos, Volantis, etc. etc.