with them clearly having known about the virus before it was even unleashed,
Wait, what?
I think there was a line somewhere in the CDC about this having been going on for a while, it had just recently gone pandemic.
Whatever happened happened pretty quickly. Our guide to this is the flower vase Shane brings Rick in the hospital while Rick is in a coma. They're new and fresh when Shane delivers them and they're dry and severely wilted when Rick wakes up from his coma in the vacant hospital. We're shown a flashback at one point of Shane trying to get Rick out of the hospital with no luck, the flowers look fairly intact here.
Giving the show all of the leeway we possibly can we'll say a month passes between Shane bringing the flowers to the hospital and Rick waking up in the abandoned hospital after the ZA has taken hold. When Shane tries to get Rick we can see that society is quickly crumbling and we later see in a flashback Shane, Lori and Carl stuck on a highway outside Atlanta when there's still "some" military action. They're stuck on the highway next to Carol, her husband and Sophia. We can assume after we see Atlanta bombed they nix the idea to go there and start to form a camp relatively nearby. (I can't recall if we see on the highway Dale's RV or T-Dog's church bus.)
Here's the big thing... Being as "fair" as possible it's unlikely more than a week passed between the hospital losing power and Rick waking up. The IV drip couldn't have lasted for more than a day after which his body would run on its own stored fat and water. In very extreme circumstances people have gone as long as a week without water and we do see that Rick is very parched when he wakes up.
Inside that week Shane formed the camp outside Atlanta, society crumbled even more, and Shane and Lori formed more of a bond and a slight romance. (We'll assume that when they had sex in the second episode this is the first, and only, time they ever did it.)
In short it seems things went downhill fast considering everything that happened likely happened within a month. We know it was a fairly short times as certain things are still working, like the backup water heaters at the police station, and going back those flowers on Rick's nightstand. Some stores and such don't seem too badly looted. (Although that's still mostly the case over a year later.) And the camp outside Atlanta has only been established for maybe a week. (Or however long you want to believe Rick was in the hospital between Shane leaving and him waking up. Again, laying on a bed exerting no energy dehydration wouldn't take hold too quickly and people have gone a week or more without drinking water in more extreme survival situations.)
As for the military, I believe the squadron The Governor ambushes were just reservists probably just doing their 2-week stint when things crashed, they didn't seem too organized all things considered nor too well trained considering how "easily" they were ambushed by The Governor and his men.
I still doubt unless we see clearer evidence otherwise any meaningful form of government still exists. If it did you'd think the Emergency Broadcast Service would be being used as well as many other means of communicating with and helping the public. Hell we've not seen so much as a banner-plane flying over them even Carol mentions that she'd "give anything" for a plane to fly overhead just to have a sense that things are still somewhat normal.
Society and government are gone. It would be nice to see the show explore this issue more, or the spin off if it happens, and I think if what I heard about the plans for this season are true that "might" happen.