Despite the wholesale return of the dead, human civilization has for the most part remained intact, continuing its ever faithful progression towards newer and better things. However, during the events of the First Outbreak, there were a few weeks when uncertainty and panic did seep into certain segments of the nation's population.
During those weeks, the basic fabric of human civilization did collapse in these isolated locales. Total anarchy broke out, vigilantes roamed the streets (at least the ones not choked with the undead); fires and looting were rampant; women, children and livestock had to fend for themselves etcetera. This Road Warrior-esque disintegration was exacerbated by the exceedingly high casualties the military sustained while first attempting to deal with the outbreak, leading to the notion that the government had failed to protect the public.
Fortunately, the government, military and citizenry of the U.S. was able to collectively step-back, take a deep-breath and regroup in the face of the undead hordes. Within three months of the outbreak, things were well on the return road to normalcy (except now with zombies).
Perhaps the most egregious example of the societal breakdown occurred in Tulsa, Oklahoma. Details surrounding the ghastly events of Tulsa are hard to come by, as the tight-lipped survivors are few and far between. Suffice it say, they know what they did, and may god have mercy on their souls.