There is significant debate among historians what the name of the current war between the League and the Terran actually is. As it has it's root in World War III, that's what they prefer to call it. However, the Terrans declared that war over before declaring a new war on Freedom Colony, which they consider 'The First Interstellar War'. Then, after the establishment of the League, the current conflict was declared. Historians which view these as separate events refer to this one as 'The First Interstellar War'. But even among this group, there are those who argue every cease-fire should be considered a separate war, which would make the current one 'The Sixth Interstellar War'.
Everyone else just call it ‘the war’.
Regardless of if you consider the war to have started when the US Economy Collapsed and World War III started, or later, it's clear the seeds for the current conflict were born out of the geo-political tensions of the 20th century. The US-Soviet Cold War laid the groundwork for West/East conflict, and then the US-China economic conflicts of the 2020s and 2030s just added fuel to the fire.
By the time China and Russia declared war on the US and Europe, no one was surprised. Tensions had been mounting for decades, with a lot of it spilling over during the 2022 Russian invasion of Ukraine. It became clear in that conflict that the United States no longer had the stomach for an armed conflict, as it's political landscape had become tumultuous at best.
(see: Western Collapse)
TBD.
TBD.
After the establishment of Calysto and The League of Allied Worlds, the newly repopulated dredges of the great western democracies (primarily from North America) set about building their new world. However, they had not forgotten loosing their homes 50 years prior. They wanted to return, in force, to retake North America. So, despite the NorAellians being very careful about the technology they'd given the League, Human ingenuity was not something they counted on. As soon as we had a working subspace engine, we set about taking it apart, understanding it, and improving it. Within a decade, we had one capable of making the journey from Calysto to Sol in three years. Sure, the Noraellians had ones that could make the travel in months, as evidenced by their help establishing Calysto in the first place. But three years was fine for a group of people who'd spent 50 years trying to make it to a star that was only a few hours away by subspace.
Once it became clear to the NorAellians what the League was planning, they did everything they could to stop it. They did manage to delay it, as the fledgling government could barely survive without their help. But the more self sufficient the League became, the less leverage the NorAellians had. And to make matters worse, there were those among the NorAellians who sympathized with the League. They sold them 'forbidden' technology, to help make sure that once they managed to take their fight to the Terrans, they would succeed.
What followed is widely considered the greatest mistake in interspecies politics. The NorAellians refer to it as their 'second greatest mistake'.
Unable to deter the League any longer, the NorAellians decided to make contact with the Terrans and give them equivalent technology to the League. If neither side had an advantage, then they would surely reconsider war. What's more is, this would allow the Terrans to establish communication with the League, and the NorAellians themselves would be more than happy to host diplomatic envoys. After all, what species ever really wanted to kill other members of it's kind? That sort of self-destruction was unnatural, after all.
Unfortunately, the NorAellians didn't really understand Humanity.
The Terrans were welcoming to their new visitors from the stars, especially once their mission was understood. They agreed that the NorAellians had made a grave error, and the proposed course of correction was amenable to them. What they didn't say was that many of them took the NorAellians arrival as a sign of their 'manifest destiny' to be the single ruling body over all of Humanity.
Diplomatic talks were started, and for the next two years, both sides appeared to negotiate while secretly building fleets of warships. By the time war was declared, the NorAellians had only just realized the mistake they'd made.
Everyone agrees that without the help of the NorAellians, the Terrans would have been forced to surrender with minimal conflict, after a mater of hours or days. While unfortunate for the Terrans, it would have saved centuries of bloodshed.
After a few intense, but ultimately inconsequential battles, it became obvious that more resources would be needed, along with forward outposts and colonies. Both sides poured all of their economies into establishing colonies as quickly as possible to ramp up their military production, and establish forward bases from which to conduct the war.
At the same time, people dissatisfied with the war now had the means to establish their own colony worlds. They headed away from the conflict, towards the galactic core. These colonies were often created by people oppressed by the Terrans, or pacifists from the League. Because so many people were fleeing both governments, these colonies were often seen as rebels needing to be brought to heel. In a stroke of genius, however, the League worked behind the scenes to convince several of the colonies to form their own loose government, and then in a unanimous vote, the League recognized this (mostly sham) government. The Confederacy of Freelance States was born.
This lead the Terrans to declare these colonies as break-away traitors, and claimed all of Freelance space for themselves. In retaliation, the Freelancers sided with the League in the conflict, and even to this day, there's an understanding between the two groups. Most Freelance pirates choose not to attack League merchants.
Over the centuries, a semi-stable no man's land of colony worlds has been established. 'The Front', as it's known, is not a formally recognized area of space, but everyone knows where it is, and those that live there know it's borders better than any map.
Colonies on the Front are often annexed or raided by either side, and while many are culturally League or Terran, which side they belong to is often complex and dependent on the current state of conflict.
It is not uncommon for most of the war's horror stories to come from colony worlds on the Front.
Right now, the League and Terrans are in a cease-fire. However, everyone expects that to end soon. Both sides have had the larges military build up in their histories over the last decade, and soon those ships will need to be used for more than minor conflicts.