I agree that the galaxy at large had grown unaccustomed to war, although it's possible there were skirmishes among the hick planets far from Coruscant. I think thousands of years of Pax Galactica made everyone kind of complacent, which is why they ignored the seedy underworld filled with bounty hunters, deathstick junkies, slavery, and crime lords. Not to mention completely missing the resurgent Sith.