FS1 portrayed Beta Aquilae as having a node leading to Sol, that presumably collapsed along with the Delta Serpentis node. The GTA would never consider any treaty that allowed a single Vasudan ship into Beta Aquilae.
Think of it in terms of the French goals for the peace treaties with Germany in 1918+ and 1945+, esspecially in regards to the german industrial regions at Rhine, Ruhr and Saar. After both world wars it was french policy to either annex these regions or have them be in a seperate entity from the a post-war german state, keeping the then economic powerhouses of the region from Germany becoming a new credible threat to french security. In both cases there were a multitude of reasons why this was not realized (e.g. British concerns for a balance of power post 1918 or the preception of an immidiate Sovjet threat in late 1940s).
GTA politics were basically a military junta and the Vasudans had Byzantine internal intrigue. Both sides would need to have their bubbles popped with a really hot needle before they backed down: think late war Japan in WW2.
I am rather thinking WWI Western Front ... while WWII in the Pacific might yield good analogues too (esspecialy on the techincal side)
Civilian colonies were nuked and irradiated, and it was doctrinally encouraged - weapons were mass produced for the purpose.
Both the Sovjet Union and the USA mass-produced nuclear weapons during the Cold War, but the existence of these weapons doesn't imply their use (officially and sanctioned). Actually the increasingly realistic threat of Nuclear weapons deployment following the so-called Sputnik Shock was lead to policy of disarmament - from the SALT-talks (1969-1979) to New START-treaty (2009).
It is not unrealistic for both sides to build an arsenal deterence weapons to pre-empt an escalation but that doesn't imply their use. The Harbinger tech and the command briefing of "Reaching Zenith" only ever say this:
Until recently, Harbingers were reserved for planetary attacks only.
"Being reserved" doesn't indicate use, it only means the weapons were stockpiled for that purpose. At this point it doesn't even mention the deployment of the Harbinger at anytime.
most effective when used in preemptive defensive strike against non-military installations.
This is the strongest evidence that the Harbinger was used on prior to the development of the Ursa as it's carrier. The "most effective when used" part doesn't need to mean that it was deployed on a civilian target, you can make that assumption from testing the weapon on simulated target and got to same conclusion - early nuclear weapon tests in 1940s did just that: Put up a dummy building (later even an entire dummy town) and see how far from the detonation point you would still destroy said building.
And then there is "preemptive defensive strike against non-military installations", which is really hard to unpack because what exactly consitutes a target for a preemptive defensive strike (i.e. an attack to preempt an attack which is currently being prepared - NOT an attack to deter a future, possible attack) if the target is also a "non-military installation", per definitionem a target that cannot execute a military attack that can be preempted?
The existence of the distinction between a military and a non-military target however re-cludes a regime to designate them. Since all current regimes to designate invalid targets are made by mutual agreement (e.g. the red cross desigating a medical facility) it stand to reason for me that the GTA and PVE at some point made an agreement on rules of engagement which contain such a provision. (In
Of Shivans and Men those are the Antares Accords)
For me this reads as a handbook entry for a deterence weapon as part of a policy of Mutually Assured Destruction. Multually Assured Destruction however is in essence build upon the premise that with both sides having the ability to destroy each other, either side will seek another way to resolve the conflict.
(Quick side note: In Blue Planet, the deployment of WoMDs against civilian targets by the GTVA is another matter because from the state of the war you can assume that the UEF doesn't have tha capacity to retaliate in kind, as such ideas such as Mutually Assured Destruction do not apply)