Albert Barnes Commentary Esther 9:3

"And all the princes of the provinces, and the satraps, and the governors, and they that did the king`s business, helped the Jews; because the fear of Mordecai was fallen upon them." — Esther 9:3 (ASV)

All the rulers ... helped the Jews—that is, the Persians, who formed the standing army which kept the Empire in subjection, and were at the disposal of the various governors of provinces, took the Jews’ side. The enemies of the Jews (for example, Esther 9:16) were almost entirely found among the idolatrous people of the subject nations. Neither the Persians generally, nor their monarchs, cared greatly for the lives of these people.