The Shadow Blades.

Despite the schism between the divided Empire and the strange occurrences that happen daily, the spirit of the Empire has never forgotten the innate strength in their ways of intrigue. Many outer warlords, from the Skull Kings to the Horse Lords never truly become a threat to them. This is due to the Shadow-Blades. Unlike the spymasters or courtly assassins, these operate differently. A Shadow-Blade will use their connections and wealth to keep an eye on enemies that are from different kingdoms and peoples. When someone becomes noticeable and poses the possibility of a threat to the Empire, a Shadow-Blade is assigned to that person. Their motto is simple; ten innocents should die than for one to grow to threaten a thousand.
The Shadow-Blade has access to the many riches of the Empire and speaks with Imperial Authority. Promising enough gold to last several lifetimes, and the protection of the Empire, the Shadow-Blade attempts to convince those who are disgruntled to murder their lieges and sabotage the key threats to the Empire. Sometimes it is an open invitation. Other times, there is the necessity of having many small steps, and pawns to destroy the greater enemy. A commoner can be convinced to leave his horses unwatched, for example. A guard may be tipped to a supposed riot, happening on the other side of town.
Those who kill for the lure of gold and a new protected life in the Empire are brought within as safely as possible. The betrayer's reward, however, is swiftness in death. The Shadow-Blades descend quickly upon them, ensuring that they cannot return to their people, or spread rumors of what had happened. Betrayers who cannot come to the Empire alive are brought anyway. Necromantic magic has often proved to be a foil to the Shadow-Blades.