Legend of the Galactic Heroes, an 110 episode anime (with a few gaiden episodes) from the late 80s to late 90s, based on a 10 volume sci-fi novel series, that was a cult hit for American anime fans. It's about an intragalactic war between the democratic Free Planets Alliance and the authoritarian Galactic Empire and has no aliens. The themes are about how governments strain, break, and change, as well as the enduring nature of war, and how humans never really change that much across history.
You can find the official subs on HiDive and the books on Amazon. You can also watch the Die Neue These adaptation from 2018 on Crunchyroll, but this isn't recommended as it's only the first season and barely covers anything.
you can get the ebooks from amazon. (8$ each, i think.) just write the names.
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Of course, there are other ways to get them (i have them in pdf, for example)....just look for them hard enough.