The so-called ComStar War stems from a clandestine conflict between the Charles Marik-led Free Worlds League and Conrad Toyama-led ComStar which resulted in a complete HPG blackout of the League. The war proved how devastating the threat of a HPG Communications Interdiction could be, with the remaining four Successor States ganging up on the hamstrung Free Worlds League.
Upon Thaddeus' death in 2820, the Free Worlds League Parliament had to choose a successor, favoring the level-headed Jeannette over her tactically savvy but more abrupt and uncharismatic brother Charles. However Jeannette had little interest in the post, making it especially clear her distaste for the prospect of leading the League in such a war-torn era, instead choosing to join the neutral quasi-religious communications organization ComStar. 
Delighted that such a high-ranked scion of a Great House had chosen to join the order, Primus of ComStar Conrad Toyama personally oversaw her acceptance into the Order. While all people attempting to join ComStar went through indoctrination sessions, due to Toyama's fear of infiltration, Jeannette's went far beyond most, with rumors of Star League-era brainwashing drugs. No matter if her intentions were honest in choosing to join ComStar, the Jeanette Marik that emerged was a fanatical believer of Blake equal only to Toyama himself. Ever a dutiful member of the Order, Jeannette made numerous recruitment trips, trading on her name and improving the public perception of the organization of the League.
Left to pick up the pieces of his father's reign, Charles ruthlessly consolidated his position and attempted to rebuild the shattered infrastructure of the League. However, in the maelstrom of the First Succession War, SAFE, the Free Worlds League's intelligence organization, had suffered considerable damage, damage from which the organization would never truly recover. With few surviving agents in Steiner and Liao territory, SAFE was not in any position to assist Charles in determining the intentions of the Lyran Commonwealth and Capellan Confederation against the League.
Desperate to overcome this lack, in February 2830 Charles met privately with his sister on Irian during one of her many recruitment trips and asked her to use her ComStar connections to intercept military communications relating to LCAF and CCAF intentions against the Free Worlds League. Charles assumed that their family ties would ensure her aid, which Jeannette agreed to supply, not realizing that she would immediately inform the Primus of his request. 
Already seeking a way to draw the Free Worlds League into the Second Succession War and to prove to Jeannette that his brother was not above the mindless warmongering that led her to join ComStar, Toyama provided her with a document supposedly from the Lyran high command containing plans for the invasion of Graham IV, Castor and Callison. Jeannette passed on the seemingly important transmission to her brother in mid-June, never questioning its authenticity. Charles refused to accept Lyran denials that such attacks weren't planned and ordered his troops into a state of readiness to launch his own attack against House Steiner. 
As Marik forces stepped up preparations to prevent and preempt the supposed Steiner invasion, the Lyran Commonwealth was forced to do the same, creating the threat that the faked documents had foretold and moving both nations to the brink of war. Thrilled at the success of this plot, Toyama revealed to the First Circuit his eventual goal. With their shattered intelligence network, the Free Worlds League would be desperate for the secret intelligence ComStar could provide, and Toyama believed this could be used to damage the FWLM and Charles to the point where Jeannette would again be the only choice for the Captain-Generalcy, making the Successor State a de facto ComStar protectorate. 
Between 2831 and 2836, House Marik won a series of grand military campaigns against Houses Liao and Steiner thanks to the extraordinarily accurate troop dispositions and movements supplied by ComStar. However for the great number of successful campaigns, there were also a number of setbacks and losses which Charles realized could only be due to his enemies receiving similar advance info of Marik troop movements. Eventually he began to suspect ComStar's role in providing similar aid to enemies, reaching the conclusion that the Order desired crippling the League to the point of requiring direct ComStar aid. Charles however lacked tangible proof, and devised a top-secret plan to expose ComStar's duplicity, Operation Cookie Jar. 
Known only to a handful of personally selected SAFE agents and the Captain-General himself, Marik visited his sister at her posting at the Class A HPG compound on Oriente in February 2837 and revealed that his troops had recently discovered a lost Star League military warehouse on Cursa. Afterwards, he secretly ordered the Marshall of Oriente to transmit the same information to Atreus using an old security code known only to ComStar. The operation culminated on March 13 when House Liao forces struck Cursa with three regiments of crack troops, who only found a virtually abandoned world. Charles Marik had confirmed his suspicions, and worse had proven that his own sister was likely party to the betrayal. Enraged, Marik ordered a strike fleet consisting of the last WarShips in the Free World League to destroy the hyperpulse generator on Oriente and kill all ComStar personnel, including his sister. On March 22 the fleet unleashed without warning an orbital bombardment which obliterated the orbiting HPG station, its 230 staff and more than 132 civilians. 
Caught completely by surprise, the First Circuit was appalled that instead of breaking the League, their actions had triggered Marik into open war against the Order. However, safe in the knowledge that only highest ranks of House Marik and ComStar even suspected their manipulation, Toyama refused outright military attacks against the League, instead choosing to play the wronged party and order a complete Communications Interdiction of the Free Worlds League until it admitted it's crime and paid three times the cost of rebuilding the station. A message publicly confirming the Interdiction was sent to every station in the Inner Sphere, followed by a private message to all ComStar personnel in the Free World League, ordering them to selectively cripple their HPGs and go into hiding.    
|β||The Free Worlds League has been placed under a full Communications Interdiction for violating the terms and agreements of the Communications Protocol of 2787. Until the League admits its violation and makes proper reparation to ComStar, in an amount equal to treble the cost of rebuilding the Oriente relay station, all communications into or out of the Free Worlds territories or protectorates are hereby suspended. So it is done in the name of the blessed Blake.||β|
|— Public message from Primus Conrad Toyama to all ComStar HPG stations, late March 2873. |
|β||This is a dark hour to test our souls and the belief in our blessed Order. All ComStar personnel in the Free Worlds League are ordered to shut down HPG transmissions immediately. Remove all key holy software and data dumps and extract the principal communications code boards from their transmitters. These devices and software will be passed on to Precentors, who will assign the proper agents to conceal the items. All personnel will abandon their stations and travel to the appointed safe houses established in Emergency Protocol 201 A. Remain hidden until further notice. Consult the Word of Blake and seek his divine guidance against any evil that seeks to corrupt and destroy our Order. The Peace of Blake be with you.||β|
|— Private message from Primus Conrad Toyama to ComStar Precentors operating in the Free Worlds League, late March 2873.|
As SAFE and ComStar's intelligence organization ROM engaged in a desperate shadow war to protect or capture ComStar personnel which quickly dissolved into stalemate, House Liao and House Steiner mounted full offensives against the Free Worlds League. With neither suffering the lack of both intelligence and communications, they captured over a dozen Marik-held worlds within six months. Desperate to strengthen worlds at risk, Charles pulled back troops from his formerly glorious conquests, allowing House Liao to recapture all the worlds it lost in the previous seven years without firing a shot. Even Houses Davion and Kurita entered the fray, like sharks smelling blood in the water, to the point that all four attacking armies were fighting amongst themselves over the spoils. In late 2838, almost two years after the Interdiction occurred and as all support for Charles evaporated, the Lyran Commonwealth struck deep into the League in seeming preparation for one massive push, finally forcing Charles to admit defeat.   
The Captain-General sent his youngest son Garth to Terra aboard the JumpShip Dark Regret under a white flag of truce. Despite Primus Toyama's hopes that the League was on the verge of collapse and would request direct ComStar aid, Garth was simply ordered to communicate that Charles was ready to accept responsibility for the destroying the Oriente HPG and pay damages. After tense negotiations, both parties came to terms in mid October and all League HPG stations, save the destroyed Oriente HPG, were online by year's end. 
- ComStar (sourcebook), pp. 24-27, "ComStar War"
- House Marik (The Free Worlds League), p. 31 "History - The Second Succession War"
- House Marik (The Free Worlds League), p. 32 "History - The Second Succession War - The Fighting Continues - The Unanswered Question"
- House Marik (The Free Worlds League), pp. 32-33 "History - The Second Succession War - At War with ComStar"
- House Steiner (The Lyran Commonwealth), p. 58 "History - The Second Succession War - Tales of Grimm"
- House Liao (The Capellan Confederation), p. 48 "History - Second Succession War"
- ComStar, p. 26 "History of ComStar - The ComStar Wars - Dark Hours, Dark Deeds"
- ComStar (sourcebook)
- Field Manual: ComStar p 12
- Field Manual: Free Worlds League p 8
- Handbook: House Marik - pg 36
- House Liao (The Capellan Confederation)
- House Steiner (The Lyran Commonwealth)