The Diadanellan Rebellion was a rebellion against the Confederacy of Borealis, which was fought on and around Diadanella between 99,963 and 99,966. It broke out due to internal desires for increased autonomy to complete independence, which had generally been ignored by the local administration of the Confederacy.
While the Confederacy suffered from smaller numbers of ground-based forces, it benefitted from near-complete superiority in space, allowing it to hold onto its primary administrative centre in Avsa and to enforce an embargo on Diadanella. Despite so, it could not hold onto territory in Diadanella's main continents, and after three years of war, political pressures resulted in the Confederacy acceding to a moderate peace treaty granting the planet significant autonomy, though not outright independence.
The E-Class planet Diadanella was first colonized directly by the Confederacy of Borealis in 99,787 as their pilot colony and potential future center of government in the Locomra Galaxy, due to its proximity to the access wormhole. The planet's population grew quickly and within 150 years, its population was nearing 10 billion human inhabitants, not including the additional inhabitants in various spaceborne colonies, moons, and other planets.
The primary source of tension between the CoB and the colonists were on autonomy: the Diadanellans wished to run their government with less CoB interference, whilst the CoB sees Diadanella as their primary seat of power in the galaxy and hence generally maintains very direct control over the planet. While the colonists participate in elections to legislatures and executive positions, these positions themselves have significantly curtailed powers when it comes to, for example, large-scale projects as the CoB would first be required to approve. All management of internal policing and military forces on the planet was also run by the CoB, often resulting in off-worlders or non-humans being assigned on rotation to Diadanella, which was almost entirely human. Additionally, the Diadanellan government was severely restricted in managing the booming colonization of the small galaxy.
By 99,960, protests against the CoB demanding autonomy were commonplace. There were already multiple political groups in Diadanella calling for outright independence from the Confederacy, attracting members with a promise of Diadanella becoming the center of an independent DDO-44-spanning entity. Most of these protests were peaceful, though they were increasingly popular with local residents as the CoB decided to gradually increase cargo tax rates to Diadanella from other colonies to pay for increased presence in the galaxy, resulting in some inflation.
In the city of Kepets, in the inland region of Ryet, a protest occurred in mid-99,962. The exact course of events were unclear, but it was believed that there were either flawed intelligence on the CoB's part or an anarchist infiltrating the protest. What was certain, however, that the independence movement DLM (Diadenan Liberation Movement) members made up a significant proportion of the protesters. Around two standard hours into the protest, one of the CoB's security units watching over the protests reported clashes involving small arms and melee weapons. In the ensuing brawl and shootout, seven protesters and four security guards were killed.
The deaths at Kepets triggered an immediate reaction from both the Diadanellans and the Confederacy. The DLM became increasingly powerful in the political discourse and many armed militia groups were formed, believing the Confederacy had fired first on unarmed protesters. The autonomy-seeking yet non-separatist group DPF (Diadanellan People's Front) internally splintered as many of its members sought to join the DLM, and the remaining members were uncertain of what course of action to pick. As DLM militias organized and began to show its presence in many cities across the planet, the Confederacy increased their security presence and those loyal to the CoB formed their own militia units, triggering the DLM to intensify their recruitment campaign and the DPF to teeter on the edge of joining the DLM.
On 7 October 99,963, a DLM militia unit rose up in arms and attacked the CoB's representative base in Kepets. As the representative building comprised mainly of civilians, the takeover was bloodless. However, in the ensuing days, as more and more militia units affiliated with the DLM took up arms, CoB garrisons began to guard the representative buildings and in several occasions low-level firefights broke out between the militias and the garrison. In turn, this triggered the formation of further militias and more violent exchanges between the two parties.
By December, the loose militias had organized into a relatively coherent force, coined the Diadanellan Liberation Army (DLA). The CoB opted to withdraw their military and policing units away from heavily rebel-controlled territory and into more loyalist areas in anticipation for a more open conflict, as reinforcements from other systems and from the Kruisir Galaxy were called in.
Small-scale firefights in streets had given way to more serious battles by February in 99,964. In this time, the DLM largely went on the offensive, as they assaulted and seized several settlements and important industrial centers from the CoB forces, while also seizing a number of advanced weapons from various caches. The DPF, under pressure from the jingoistic populace, began raising their own armed units which operated semi-independently from the DLA.
The vast interior of the large continents Pasa and Marmara had largely been evacuated by the CoB by May, while they held onto more defensible positions closer to the ocean. As the Diadanellan rebels lacked significant capability in space warfare, they were unable to insert forces behind the Confederate lines, while the CoB had the full capability to do so. The CoB's capability to launch tactical space bombardments also restrained the DLM from conducting a serious offensive against their planetary positions at first.
Eventually, the DLM managed to gather enough strength to launch a large-scale offensive aimed at pushing the CoB forces into the sea between August and October. While this offensive managed to force the CoB to evacuate significant proportions of its land forces, they managed to hold onto several key strongholds thanks to extensive use of spaceborne interdictions. As the year came to a close, the CoB managed to somewhat expand its held territory as the reinforced CoB forces pushed the expended DLM back. During this process, the DPF largely refrained from conducting offensive warfare, and acted more as a garrison force or on coastal defense.
Small-scale fighting continued in the first half of 19,965. During this period, CoB blockades in space gradually eroded the populace's willingness to fight. By August, several DLA attempts to bypass the strongholds and directly invade the still fully CoB held continent of Avsa by naval invasion had failed, due to both space and naval interdictions. Increased CoB presence ferried into the strongholds also reduced the DLA's capability to maintain their full hold over the continents, and they struggled with an increasingly war-weary populace feeling threatened by the possibility of a DLM conscription. The DPF, reading the populace's mood, began to reach out towards the CoB for a potential peace deal.
On November 99,965, the CoB launched a major offensive which managed to push the DLM forces away some 300 km away from their previous frontlines. This severely reduced the DLA's combat capability due to loss of equipment not immediately replaceable, as CoB had intentionally sabotaged potential weapons manufacturing facilities during their retreat. In the meantime, negotiations were approaching a conclusion with the DPF, and due to the offensive's results, the DPF decided to accept the CoB's offer for increased autonomy instead of complete independence. On the new year of 99,966, the DPF and CoB released a joint statement declaring ceasefire between the two parties, putting the DLA in an awkward position as their forces were already stretched in the frontlines, and would be unable to maintain a full garrison hold over the vast continents. This forced the DLM to begrudgingly agree to a ceasefire just one week afterwards.
In orbit around Diadanella, the CoB generally held absolute superiority throughout the course of the rebellion, save the occasional raids of DLA's small and hastily assembled atmospheric fleet, which lacked large spacefaring vessels. For the most part, they did not pose significant threats to the CoB orbital bombardments, and generally focused on interdicting high-value supplies to disrupt CoB ground forces.
The rebellion formally ended on 21 February 99,966 with the signing of the Imbrosian Settlement, containing clauses increasing Diadanellan autonomy, such as reduced numbers of CoB appointees and increased rights for Diadanella to manage colonization projects in Locomra. The settlement were signed by just the DPF and the CoB - the DLM leadership went into exile along with some DLA soldiers and a large number of sympathetic civilians. They settled in a nearby system on the moon of Estherhav, establishing a colony which under the terms of the ceasefire would be permitted to have virtual independence in governance and significant colonization privileges.