Misconceptions about the League
OK, you guys are doing a lot of speculating without having a whole bunch of hard data on which to base your prognosticating.
Now, I (obviously) have a lot more data than you do, and I (equally obviously) am not going to hand all of it over to you without making you buy the books. However--
First, those of you who are arguing that the vast majority of the League's system defense forces are not -- and have not been, for centuries -- in serious "defense mode," are essentially correct. Very, very few of the League's systems see any need to have anything except the equivalent of Coast Guard cutters (LACs). Expecting them to have anything more than that would be rather like expecting St. Louis to have the squadron of Arleigh Burke-class destroyers because an enemy invasion force might possibly make its way up the Mississippi Valley. It's just not any sort of real priority for the huge bulk of League star systems. Why should it be? There are a limited number of systems which have specific reasons for having more powerful defense forces, either because they have something especially valuable that needs protecting, or because they happen to have largish merchant marines for which they provide a significant amount of security, or they have system political leaderships which are either paranoid (where their neighbors are concerned) or potentially avaricious (where their neighbors are concerned). That number, however, is extremely limited as a percentage of the League's total membership.
Second, the population estimates being handed out for many of the League star systems are for the most part high. True, the Star Kingdom's population densities are low, but don't forget two things. First, we know that one of the attractions of the Star Kingdom for Allison Harrington was that there were no restrictions on family size. Second, in the case of the League, we are definitely talking about highly industrialized societies, and the tendency in industrialized societies here on Earth has been for family size to fall, not to increase. While a highly industrialized, space going star system can easily support the population in the billions, there's not going to be very much pressure for those populations to be in the high billions. Most of the star systems in the Republic of Haven are going to be at least as densely populated as the majority of League star systems.
Third, while certain events which transpire in At All Costs are probably (please note the conditional) going to cause at least some of the League's military planners to begin to stir sleepily, if not quite wake fully up and smell the coffee, the stupendous inertia of League military thinking is literally almost impossible to overestimate. There are certainly elements within the League which have been looking much more critically at the evolution of military technology and doctrine in the Havenite Wars, but they remain a very, very distinct minority. They're the sort of people who write articles for the Naval Institute Proceedings warning that nuclear-powered carriers are dangerous, vulnerable, obsolete, expensive white elephants in an era of increasing use of pilotless aircraft. They may or may not be correct, but the mainstream of League naval thought is going to dismiss them as alarmist cranks. Eventually, people will start listening to them, probably in increasing numbers. The problem is that it's going to take something drastic and unpleasant that happens to the League for that to happen. Until that, the League is going to persist in viewing the war between Manticore and Haven as the equivalent of the Iraq-Iran War. Of course it's dragged on forever, since the people involved in fighting it simply aren't very good. And of course the casualty numbers have been atrocious (although undoubtedly grossly exaggerated in the popular media)! Those hapless neo-barbs are probably using the equivalent of human wave tactics! And they're such barbarians that their probably also using the equivalent of chemical weapons, and you know what kind of casualty figures that would produce!
Fourth, at least some of the people in the League who do have a better idea of what's going on out Manticore's way are deliberately downplaying the threat. Without going into any great amount of detail as to who these people might be, I'll simply say that their various nefarious plans would not be advanced if it should happen that the Solarian League Navy (or any significant number of SDFs) should suddenly feel inspired to begin building any first-class, modern fleet.
Fifth, membership in the League (except for those planets which are essentially captive provinces under OFS rule) is entirely voluntary. There is a specific mechanism for star systems to leave the League, and there is no mechanism for compelling star systems to remain in the League. In fact, compelling star system to remain in the League would represent clear violation of the League constitution (such as it is, and what there is of it).
Sixth, there's a lot of reason to believe that--
Gotta go! [G]