―Magnus rallying the populace of the colony world to fight against the UNSC invasion.
The Tannis Uprising was an event that took place in the winter of 2572, and was seen as one of the first major battles in the First Galactic War, in spite of the fact that Legion troops were not involved in any way. This was also notable as the first live combat deployment of the SPARTAN-IV X-Ray Company. The uprising lasted for over two months, with prolonged guerilla fighting and hit-and-run attacks, before the remaining Insurrectionist troops either escaped or surrendered to their foe.
Though it was considered a victory for the UNSC, the heavy-handed tactics used and moral ambiguity of their invasion sparked major discontent among the populace of many other planets, Tannis itself having a long history of rebel action in the following years. Following the conflict, the mysterious rebel only known as 'Magnus' was put on the UNSC's most wanted list, his very existence having only been speculation for years before in connection to other uprisings and terrorist attacks, the mysterious figure having previously thought to have been a myth or byword for a group of people. It was this engagement that was generally seen as the catalyst for mass revolt and the extension of the war, which transformed the Legion from a conglomerate of rebel forces to a unified military with it's own backing due to extensive support from the outer colonies.
Colonised in the mid 25th Century, Tannis was one of the few outlying colonies that survived the Human-Covenant War untouched, largely due to the fact that it was out of the way and had little strategic value, aside from it's agricultural operations. As one of the outer colonies, the assumption was made that the Covenant would attack. However, as the years went by, and assaults were made into the inner colonies, it appeared that the Covenant had either missed or forgotten the world, leading to most of it's defence fleet being redirected to other engagements, leaving the colonists to fend for themselves.
Seemingly abandoned, a lot of anti-UNSC resentment was built up on Tannis. There were nearly twenty thousand people living there by 2553, when the war officially ended. In the following months, UNSC ships arrived in the area, and were surprised to find that the colony was still thriving in spite of it's relative isolation. Though there had been scattered bursts of communication over the years, it had been assumed that Tannis had been glassed in the 2540's. Within a few months, UNSC troops had landed with the intent of helping the colonists, though they were met with some degree of discontent, largely from the older part of the populace.
Aside from sporadic, isolated incidents, Tannis was peacefully integrated into the UNSC once more. By 2565, an orbital elevator had been constructed in the capital, allowing for the easy transport of materials and supplies. This was seen as a great boon for the colony, as it could deliver much-needed supplies into the devastated inner colonies, leading to a period of prosperity. However, there were various taxes and other laws set into place regarding trading, with the military taking over the orbital station to regulate supplies. To the largely independent colonists, this was an offence after many years of being alone.
With tensions rising in the late 2560's, several groups emerged on Tannis with an anti-UNSC and UEG stance. Most were largely peaceful, or merely wanted less control over supplies, but there were some who took stances familiar to that of older Insurrectionist groups, wanting full independence from the UNSC, reasoning that the colony had gotten on fine without support for over a decade. With more outbreaks of violence among the settlements, UNSC marines were called in to keep order, though this only served to escalate things. By 2572, and the outbreak of a Civil War between the UNSC and a dozen of it's colonies, things on Tannis finally came to a head.
While there had been a few outbreaks of violence across the planet, the first major event that begun the uprising in full was on October 9th, when twenty seven colonists, led by Alfred Bates, a lieutenant in the old Tannis militia, attacked a guard post. The men held only a few guns, relying mainly on numbers and surprise, as well as model weapons to make the marine squad surrender, giving them access to the armoury. After looting the outpost, Bates allowed the marines to escape into the night, and began to pass the stolen weapons between several safehouses, before setting the outpost alight as a sign of defiance.
The next morning, UNSC marines came down hard on the local towns surrounding the outpost, launching dozens of raids in order to find Bates. Though these were unsuccessful, he was stopped at a roadblock that evening and promptly arrested. He was incarcerated in a local prison with several of his collaborators, and beaten when he refused to give up any information. However, the planetary authorities did not report his arrest to the general public until they were sure there would be no retaliation by his subordinates.