This one meant Aquilonian under Aquilonian command. Aquilonia is an aggressive, expansionistic empire rules by corruption and greed hiding under Mitra’s smile (when not rules by Conan, which it obviously isn’t at this time). They also hate Stygia and anything Stygian adjacent, such as a Stygian arch - mage’s personal artifact dig site.
They are there to loot and pillage, before Toth-Amon does. The only way to keep powerful relics out of Stygian hands is if they take them by force first. Something something something, if we don’t invade the Exiled Lands the snake cultists win.
Mercs can be anywhere and everywhere and may be better and random encounters.

Also, lore wise, the Purge is Toth-Amon sponsored looking for Relics, not Stygia sponsored looking for cash money…
Until this update.

Future updates may equally rewrite the particulars.