Directive 21 was touted as a measure to curb the activity of pirates on border worlds of the Star League; in truth, it was a response to the covert armament programme initiated by the Outworlds Alliance Minister for Trade (and later President) Grigori Avellar in anticipation of the Star League invading the Outworlds Alliance. Cameron issued Directive 21 when he became aware that the Outworlds Alliance was procuring BattleMechs for the first time, and the SLDF and DCMS troops deployed into the Outworlds Alliance were an attempt to hunt down these BattleMechs. 
With the Star League High Council ignoring the official protest of Alliance Prime Minister Catherine Avellar and the Alliance lacking either the military might or moral backbone to oppose the occupations, three worlds within the Outworlds Alliance were forced to accept military garrisons ; the worlds of Bad News and Niles were occupied by troops from the SLDF VI Corps, whilst Santiago was occupied by troops from the DCMS. All three worlds were considerable distance from any reported location of pirate activity.  
- Historical: Reunification War, p. 108, "Something From Nothing"
- The Periphery, p. 25 "History - Star League Era - Rebellion in the Rim"