Coming during the final years of the Reunification War, the Freebooter's War (2584-2588) was a short uprising by the units of Shepperton's Grenadiers in apparent discontent over the disposition of the Andurien worlds. The conflict lasted almost five years, during which the Freebooter ’Mechs ranged with impunity along the Free Worlds League - Capellan border.
As the Reunification War campaign against the Magistracy of Canopus drew to a close, elements of the Capellan Confederation grew increasingly wary that the increased volume of Star League Defense Force and Free Worlds League Military troops in the Andurien region showed no sign of leaving, with Capellan "patriots" believing this proved Houses Cameron and Marik were secretly conspiring to cede Andurien back to the Free Worlds League. 
In response, a group known as Shepperton's Freebooters struck at Free Worlds League worlds in and around the Andurien province. The Freebooters were careful to avoid worlds with an SLDF presence, disrupting infrastructure and the local economy while the Captain-General was still busy with the SLDF campaign against Canopus. While the NIA and HCID quickly identified the Freebooters as being predominantly deserters from the Capellan Confederation Armed Forces and demanded the Confederation deal with the problem, the high level of popular support for the Freebooter's "just" actions meant the CCAF and Maskirovka made only half-hearted attempts to stop them.
Furious at the continuing problems, Captain-General Marion Marik sent a strongly worded comminque to Chancellor Ursula Liao demanding that action be taken, angered at being dressed down such a fashion Ursula threatened her military and intelligence chiefs with execution, finally prompting them to make a true effort to stop the threat. As the CCAF was finally able to beat back two raids, a combined Maskirovka and Star League Intelligence Corps operation tracked a Freebooter's vessel to the world of Wisconsin. As the CCAF prepared to launch a strike against the world, Marion's son, Ian Marik, acted under his mother's authority and demanded a FWLM presence in the military campaign against the Freebooters, sending the 1st Free Worlds Guards. 
The attack on the Freebooters began on the 19th of March 2588; the two light battalions the Freebooter's could muster faced the combined strength of the 1st Free Worlds Guards and Capellan's Sheng's Chasseurs, and in less than a day the Freebooter's were either dead or in captivity.
The commander of the Guards now found himself facing a new problem; the Freebooters called en masse to be taken prisoner by the League, rather than the Confederation. The Chasseurs insisted that they had jurisdiction over the prisoners because the prisoners were Capellan citizens, and as deserters the prisoners would be executed. Colonel Appleton of the Guards asserted that as the crimes had taken place on Free Worlds League soil, the League had prior claim. Present within the Guards was 19-year Lieutenant Rhean Marik, daughter of Brion Marik and future Captain-General of the League; already highly knowledgeable on both Free Worlds League law and Star League law, Marik highlighted that the prisoners were in fear for their lives and that imprisonment in the Free Worlds League would not be a soft option. Her presence and determination threw Sheng off-balance, and Appleton managed to capitalize on this and negotiated an equitable agreement with his Capellan counterpart. Half of the prisoners were assigned to the Free Worlds League, and spent the next 20 years in prison. The other half were assigned to the Confederation, returned to Capellan space with the Chasseurs, and were beheaded in front of Chancellor Liao on Sian on the 19th of August.
- Handbook House Liao, p.24, "Timeline: The Age of War and Star League"
- Historical: Reunification War, p. 103-105, "The War At Home: The Freebooter's War"