In the 2570s the newly formed Star League was divided between Hawks, intending to complete the unification of humanity by force, and Doves, who felt that a continuation of diplomatic approaches was wiser. Marion Marik and Ursula Liao were among the latter, Hehiro Kurita and Alexander Davion the former.
But what if Alexander Davion felt that another war was not in the best interests of the Federated Suns. It would inevitably strengthen the Star League's centralisation through 'temporary wartime measures' after all, and he'd been determined to maintain the prestige of the Federated Suns despite joining the Star League. Also the most dangerous Periphery State was the Taurian Concordat, his immediate neighbour. He was the most likely to face retaliation and no matter how victorious the Star League might be later on, he could hardly have liked the idea of taking the brunt.
So let's suppose that Alexander doesn't back warfare as a solution. It had taken thirteen years to bring the six current members to agreement and two more years of negotiation to come up with the Star League accords. Surely the Periphery states were worth at least that much investment of time and energy. The Rim Worlds Republic would be a good starting point, House Amaris was already pro-Terran so quiet support of his legitimate government could hardly be objectionable.
In pursuit of this, Alexander recommends a reduction in emphasis on the SLDF. Clashes on Robinson and Milos make it clear that the SLDF had a long way to go before it will be accepted. Rather than being advertised as a 'show of strength', the United Triumph exercises in 2572 are billed as an exercise in learning, essentially fault finding. The SLDF does not appear to be a well-honed military machine capable of crushing the periphery and tensions relax slightly. Later that year, when it is discovered that the Outworlds Alliance had a modest force of BattleMechs, rather than reacting with alarm, Alexander convinces the Star League Council that absent a clear threat the Alliance Militia would find little support among the pacifistic Outworlders. In fact, he considers them a welcome market for aging military equipment that the AFFS was still burdened with. Selling it to the Outworlds would make room for the scaled-back AFFS Army and Navy to standardise a higher quality of hardware and even slightly offset the costs.
Another near crisis emerges at Malagrotta but the FSN, well aware that their Prince was not spoiling for a fight, react relatively cautiously and the situation was defused. There is even some good press with the Federated Suns warships having provided aid to Taurian spacers in need.
Without these spark points, the Star League does not face the same drive towards war and the Star League didn't impose the significant taxes and tariffs on trade with the Periphery that in canon proved very damaging to both sides. That in turn means that Viola Steiner is unlikely to move to the side of the Hawks and therefore the Pollux Proclaimation never happens. There might even be some equivalent that simply asks that the Periphery states accept it if one or more of them chooses to join and promises not to use force to drag them in.
This may in turn lead to no Manchester Directive by Gregory Amaris, which combined with fewer economic problems may soften attitudes in the Rim Worlds Republic. It's unlikely to produce much of a pro-League faction but it's likely to delay that pot coming to the boil. And once it does, the SLDF won't have other commitments, so it's just possible that they might be able to move in to rescue Amaris, help him restore order and then very publically withdraw until such time as he joins the Star League, which he would no doubt do quickly. Thus the Rim Worlds stand as a full member of the Star League...
How might the OWA, MoC and TC react? Might House Kurita start pulling away from a Star League where their leader is increasingly isolated?
