First Hidden War
While essentially a decades long high-stakes conflict between Star League and the Draconis Combine, the one-on-one dueling nature of the so-called First Hidden War barely disturbed the political serenity of the Star League era.
After the conclusion of the Reunification War, many in the Star League welcomed the prosperity of the supposed Good Years, but underlying tensions and disagreements bubbled beneath the surface, exploding into the open in 2650 when reports reached Terra that Tadeo Amaris, leader of the Rim Worlds Territorial-State, was expanding his personal army at an alarming rate. Michael Cameron, having recently succeeded to the title of First Lord of the Star League, convened a special meeting of the Star League High Council, whom he persuaded to issue the Council Edict of 2650 restricting the size of personal military forces that any League member could raise.
Despite the benefits of the Star League, many in the Draconis Combine viewed joining it as a failure. Increasingly isolating itself from the League with the rise in the use of Japanese language and culture in the Combine, House Kurita's belief that the Camerons had drafted the Edict in part to prevent the Combine from growing too powerful, and unable to protest it more strongly lest their role as Tadeo Amaris' secret supplier of military hardware came to light, only helped to further fuel the divide.
The upsurge in interest in the medieval culture of House Kurita's ancestral homeland also wrought many far-reaching changes across the entire Draconis Combine, including its military. Already viewing themselves as a class apart, the Kurita MechWarriors soon styled themselves in the manner of the ancient samurai and wholeheartedly adopted the tenets of Bushido as their own. A side-effect of the Combine warriors' focus on Bushido was a fascination with dueling, initially with swords but soon between BattleMechs became the norm. The Combine's MechWarrior regiments fought brutal live-fire contests to determine who was the best warrior, the DCMS high command allowing the duels as means to sharpen and refine their forces during the peacefulness of the post-Reunification War period.
When the Edict of 2650 came into effect the DCMS was forced to officially dismantle many units including several BattleMech regiments, but they allowed each warrior to take their weapons with them and reassigned them as "civilian bodyguards" to nobles in the Combine government. Effectively without steady employment, many of the masterless Ronin fell back on their skills to survive and the tempo of duels increased, with a number becoming champions known across the Combine. Eventually the best and boldest warriors began to challenge warriors from the SLDF regiments stationed in the Draconis Combine. 
At first the Star League forces resisted, but in 2681 the resolve of a MechWarrior of the SLDF fort on Benjamin broke and he went out to challenge one on the ronin, with SLDF forces watching in horror as the Combine MechWarrior easily dispatched and killed him within ten minutes. With more duels with similar defeats following this, First Lord Michael vigorously protested to Coordinator Urizen Kurita, who in turn threw up his hands and blamed the Edict of 2650 for making them ronin and insisting they were "beyond" his authority. While politically dangerous, the Coordinator viewed the SLDF troops in his realm as an occupying army and secretly approved and aided the actions of the ronin, hoping that humiliating the best of the Star League would further cement the Combine people's belief in their superiority to the "outsiders".   
Despite the seriousness of these events and the Combine's state-run media hailing each victory with extensive coverage, except for those who lived nearby to the fortresses the duels seemed to be the stuff of romantic fiction, lending the entire conflict an unreal quality that barely disturbed the general level of peace across the Star League. But by 2682 with five SLDF MechWarriors dead and twelve wounded in duels, the First Lord more than recognized the increasing damage to the reputation of the League and its military, triggering fears that the Combine had discovered some secret new technology and ordering one of the ronin 'Mechs be captured at all costs. After a hapless ronin was forcibly taken on Leiston, his 'Mech was rushed to the Terran Hegemony to be examined, only to reveal nothing unusual about the 'Mech's construction or capabilities.
Finally realizing the ronin simply had superior training than the warriors of the SLDF, the First Lord ordered his troops to refuse all dueling challenges until further notice, with the delighted Combine making oblique references to the seeming cowardice of the SLDF. In fact the elite of the Terran Hegemony military were secretly undergoing extensive training as part of the Advanced Combat and Maneuvering Skills Project. Ranging from ancient Oriental martial arts philosophies to advanced neural through technologies, these warriors were almost completely retrained in piloting of a BattleMech, with the fifty-two warriors of the first graduating class becoming the SLDF's first champions in 2687.
The Champion of 75th Royal Hussar Regiment stationed on Minakuchi was the first to face the ronin, fighting for over an hour and forcing the showed Kurita MechWarrior into a draw, followed ten days later by Lieutenant Karen Graham defeating a ronin MechWarrior in her Phoenix Hawk on Awano. Rather than discouraged by these defeats as hoped, the fact that the SLDF now had warriors worthy of fighting only made the ronin even keener to duel. Recognizing that he could not prevent the duels, the First Lord now sent envoys to the Combine bases, not to challenge but to offer the ronin commissions in the SLDF. Though an outraged Urizen was unable to prevent this as Executive Order 34 forbade him from interfering with SLDF recruitment, only a few accepted the First Lord's offer, but those that did became instructors at the ACMS program and further enhanced the SLDF Champions training.
The dueling between the Combine and the Star League forces continued on and off for the next fifty years before trailing off during the reign of Simon Cameron, with a final tally of House Kurita winning 49% of the time, the SLDF Regular Army 47% with draws constituting the remaining 4%. 
The Advanced Combat and Maneuvering Skills Project was eventually renamed as the Gunslinger Program and became an important part of the Military Academy of Aphros, training the elite of the SLDF.  The First Hidden War would also help to fuel the media's interest in 'Mech on 'Mech dueling that would become the Solaris Games.
- House Kurita, pp. 48-49 "Bushido and BattleMech Dueling"
- Star League, p. 58 "First Hidden War - Urizen's Scheme"
- Historical: Reunification Wars, pp. 167 "Aftermath - Hidden Wars and Increasing Discord"
- Star League, p. 59 "Urizen's Scheme"