Originally posted by BlackMage11:
How much weight would you place upon the Imperial Navy for failing to corral the Rebellion when it had the opportunity?
The Imperial Navy was vast and well-disciplined, however, that does not necessarily work to their advantage. The old military axiom comes to mind here: "The insurgent wins by not losing, the army loses by not winning." For all their might, the Imperials lost not because they were stupid, but because they were too conformist, too unimagenitive; and that doesn't even touch on the many talented Imperial officers who defected to the Alliance. General Crix Madine, who you see in the briefing room in ROTJ, was one of the Empire's most ingenious covert specialists becore joining the Alliance after Hoth.
Also, though this is not covered in the films, the victory at Yavin 4 was really the first coup for the Rebellion. Before that, though they were themselves well-disciplined and -trained, the Rebels simply did not have the size nor the opportunity to really show up the Empire. They were a thorn in the Imperial hide, surely, but up till then the engagements of the Galactic Civil War consisted mostly of small-unit affairs, not unlike the French Resistance during WWII.
Also, bear in mind that there were several notable defeats for the Rebels, both before Yavin, and in between Yavin and the near-rout at Hoth. Derra IV is probably the best known; an important Alliance supply convoy, bound for Echo Base on Hoth, was interdicted by the Empire at that world and utterly destroyed.
Also, would you attribute the technological inferiority in starfighters, particularly between the X-Wing and the TIE Fighter, to the Empire's major defeats?
The TIE Fighter was not necessarily "inferior technology", but instead the result of the Emperor's personal military philosophy. Palpatine, who fashioned himself as the center of Imperial authority, naturally had a hand in designing the Empire's armed forces, and be was a firm believer in quantity over quality. The TIE Fighter and its variants were the best personification of this philosophy that the Imperial war machine could come up with.
That said, the TIE Fighter, and its later variants, could be deadly dogfighters in the right hands. It was more maneuverable and faster then the X-wing; even though one-on-one the X-wing was the superior starfighter overall, the Empire's swarming tactics favored the TIE. The difference, in the long run, was that the increased survivability of Alliance starfighters over those of their Imperial counterparts enabled the Alliance to amass a force of experienced veterans who grew to trust and rely upon their machines, so that by the Battle of Endor, your average Rebel fighter squadron could be worth as much as three Imperial squadrons, depending on type, level of experience, and other factors.
This doesn't quite take into account the Rebels' and Imperials' newer fighter models, but the base formed in prior engagements would help the Rebels to further turn the tide of the Galactic Civil War after the death of Palpatine.
I could go on for quite a while, touching on tactics, overall strategies, leadership or campaign inertia, but that could last for hours...