From a post to ALT.BOOKS.DAVID-WEBER dated September 20, 1998:

What happened to Erewhon's League Membership?

    Erewhon never had "League membership" in the sense of being a voting member of the Solarian League. What Erewhon, and several other junction termini star systems, had was a special treaty relationship with the League, a sort of NATO membership. As a general practice, these single-star polities are considered to have League "membership" because they receive technical infrastructure support, very favorable economic relationships, and mutual defense military treaties with the League. The League would prefer outright annexation of all star systems at the far end of wormhole junctions which connect to League territory, but several things mitigate against this. One is that the League's own foreign policy makers are prone to divisions and internal squabbling (remember; the vast majority of League citizens are rather like the majority of present-day U.S. citizens. As long as there are no other superpowers, as long as the economy is strong, and as long as the rest of the world leaves them alone, their primary concerns are domestic, and foreign policy is often seen as irrelevant or even as a distraction from issues of "real" importance.) Another reason the League doesn't go around annexing everyone in sight is that single-star polities like Erewhon realize perfectly well that they can get more out of the League by remaining independent and requiring constant "courting" than they could get as one more League member, submerged in the great morass of other members and no longer provided with a special status to secure advantageous treatment. What happened in Erewhon's case, however, was that the Erewhonese's ability to get special concessions from the League fell afoul of the League's fundamental pacifism. As the People's Republic kept aggressively expanding in their direction they became--just as the Legislaturalists had feared might happen--apprehensive about what the Peeps might have in mind for them. But whereas the Peeps had been afraid that the League might actually honor its treaty obligations and act militarily if the Republic went after Erewhon, the Erewhonese had what they considered to be mounting evidence that the League would not act to preserve Erewhon's independence if that meant war with the PRH, and especially not if the Peeps offered the League a sweetheart deal for accepting new ownership of the wormhole terminus. (This evidence consisted of the League's failure to support Erewhon's protests as the Peeps nibbled away at star systems between them and Erewhon, and--to be completely honest--was also the result of some very adroit Manticoran diplomacy... and quite a few "black ops," including some Erewhon still doesn't know a thing about.) As a result, the relationship which obtained at the time of On Basilisk Station was actually already in a steady state of decay (although few outside observers realized that), and Erewhon eventually decided to throw in with the Manticoran Alliance. Roland Green's story in Worlds of Honor will deal, tangentially, at least, with Manty-Erewhonese relations during this period of change but prior to Erewhon's joining the Alliance.