@not_gagarin
My own recommendation is to start Cherryh’s #AllianceUnion books with her 1980 Hugo winner ‘Downbelow Station’ which is somewhat mid timeline but also the book that really kicked things off.
There also very deep prequel ‘Alliance Rising’ with her partner Jane Fancher which is the most recent edition, and could be a good entry point.
The huge novel ‘Cyteen’ is often recommended as a starting point, but it’s also a huge spoiler for ‘Downbelow Station as it dives deep into the Union side society, and takes place after the turning point that is the focus of that book.
The Chanur books exist in the same universe it seems, but don’t really interact with the Alliance-Union ones.
Then there is another very long running ‘Foreigner’ series, separate again, which is focused on a human colony marooned on planet inhabited by in indigenous sentient civilization. It’s focused on diplomacy and social interactions.