There is the two fighting sides, the Federation which proudly boasts its capital planet as Earth. Then there is the Union, which was once fringe worlds that pulled together and made an alliance to get out from under the thumb of the Federation. It's been almost 100 years since the Union declared their independence and won a war for it. Naturally there has always been tension between both factions. Even so people carried on and continued to expand and take new worlds as their homes. The central Union planets are no longer on the boarder and years of espionage and R&D has put both factions on the same level give or take technology-wise.
The Federation tries to tout itself as a near-utopia with shining clean cities with continuing humanity's progress in the universe. The kind of place where propaganda tries to make people feel proud and nationalistic about where they came from and have them rise up and join the military and do your duty to your people. The real fact of the matter is that things are starting to stagnate and crumble in the Federation.
The Union isn't any better. Corporations found a nice home in a place that was trying to push off the shackles of a large domineering government. They try to make it seem like anyone who is clever and can start a business can succeed. There was one point where that was true, but now it's an extreme rarity. Money talks and the poor get screwed.
When the new war started both sides clamped down and sucked any fresh new border world up that they could on short notice taking them for people and resources. Now with the war going strong for 10 years, their grips on the ever expanding border worlds gets exponentially looser the further you go from their declared territories.
