As I understand it, the Terrans had very little else to do in the 60 years of isolation other than factionalise after the Lucifer incident, as people saw the opportunity to seize power from the severed GTA and replace it with a more modern, realistic Earth Alliance whose politics, internal structure and regard to the substantially altered economy of the Sol system. In short the GTA needed to be replaced to deal with the isolation enforced on the population of Earth and her colonies.
Of course, being stuck in Sol with a growing fleet of interstellar warships intended for use against another hostile alien race (both Vasudans and Shivans being the historic factors), the desire for expansion set in with the EA leadership. It eventually became clear that something or someone was trying to reach Sol as the EA's sensor nets began to detect subspace emanations from the presumed collapsed Sol-Delta Serpentis jump node. These were, of course, the early experiments in the Melia (Sol Gate) project to establish a positive subspace link with the Sol system. Seeing the chance to finally leave their increasingly cramped home, the EA fleet readied itself to carve out a new interstellar empire and began building the Icanus to safeguard against another Shivan superweapon and secure Sol while the fleet at large would further the interests of the Earth Alliance.
Although contact with other Terrans was perhaps expected (the visitors through the Sol Gate could have been Terrans, Vasudans, Shivans or some other race), the differences between the new generation of hard-worked, isolated, resource-starved and the relatively pampered, comfortable Terrans of the GTVA didn't help resolve the differences between the organizations. And so, the opening stages of the war occurred.
As for the Vasudans who escaped the cataclysm of the Lucifer, they were war heroes and regarded as such. The people of Earth weren't broadly anti-Vasudan on the whole, but the scar of the Fourteen Year War was still present for those groups who were explicitly anti-Vasudan (and whose branches outside the Sol system were undoubtedly somehow affiliated with the NTF). There was no enmity on the Vasudans' side - after all, they had lost their own home and were readily adopted into Earth culture after risking their lives to save it.
EDIT: This isn't official, although the way I wrote nearly all the technical, briefing and mission stuff in Inferno, it could well be.
