There wasn't an earth bending Avatar. He or she died young (probably 5 to 7ish), before anyone figured out he or she was the Avatar. The world has named that Avatar the Spirit Avatar. Most people didn't know the Spirit Avatar had died though, and after years of waiting, the avatar faded into a distant memory.
From what I've found out, Korra died around 20 years ago. During the gap between when Avatar Korra passed and when the new Avatar would be discovered, society fell into disarray, the world unbalanced. The people in power became tyrants, and the lives of commoners like me changed drastically. Food and power were no longer available. Hospitals eventually shut down, followed by the police. Their (the police) forces became too thin, spreading out to try and cover all of the riots and raids made for human necessities. Since then crime has only increased. Most people moved out of cities and into the countryside, farming for themselves and staying out of danger (for the most part). Disease spread, a nasty plague, wiping out a lot of the world's population. People then started separating back into their element's territories. Fire in the Fire Nation Islands, Earth in the Earth Kingdom, Water in the Southern Ice Villages and the Northern Water Tribe, and Air to Air Temple Island (they stayed where they were, being only about 20 of them).
No one really knows what happened to cause society to fall to pieces. The only explanation is that the Spirit Avatar didn't serve it's time in the world, throwing off the balance of the world. It's surprising how fast things fell apart though. There must have been some serious gouges in the foundations of society before everything came crumbling down. But the leaders of the world just painted over the cracks and moved on with their self-righteous lives (sorry, possible exaggeration). I (nor the rest of the world) know a lot about past history, or fact from fable. But from what I gather, before the GAP (Gone Avatar Period, trust me, I didn't make that up), society was (mostly) fully functioning.
Nowadays, major cities have become more orderly, providing measly food rations and health control (not the same as health care, health control is the act of keeping negative health influences out, it doesn't help people once they are sick). Some even have electricity, and developing new technology (some of which is pretty impressive: moving pictures, long distance talkie things, portable music players, flying vehicles, etc). For the most part though, except for the developing cities, the world has gone backwards in development.
Mostly now all people have is hope. And although new life is usually considered hope, lots of children are orphaned or abandoned, and die infants. Somehow, even though I was either orphaned or abandoned (I can't remember what), I survived. The earliest memory I have is me living in a cave searching for worms and other crawly insects to eat. I was young then. But this isn't unusual. Many children are in the same situation or worse.
So now a word from me to you. There are not many non-benders alive. So sorry to you pro-non-bending-people out there. With most people fending for themselves, you pretty much die without being able to use an element. Me, I migrated down south when I was about seven or so. The villagers don't particularly like having a fire bender around, and I have to be careful of where I bend. Other than that though, I'm doing pretty well.
Oh, and I lied (I tend to do that). I do know who the Avatar is. He's a fire bender. He is the next Avatar after the Spirit Avatar (I think), and no, he has not been hiding from the world. He has been dying, like everybody else (okay, if we were all dying, we would all be dead, but we surely ain't living much either).
By the way, I haven't been dying (lately). And I am not of the male gender. Just putting that out there.
Okay idiots. This story isn't about me. My life is not about how I am the Avatar and I have to save the world from a horrible danger and if I don't the world will end. And no, it is not about how I am in love with the Avatar, and he has this important calling and so we can never have a deeper relationship than friends and how I wish it was going to work out, or any other Sue stories you can think of (and no, my name is not Sue). This, what I am writhing now, is the story of the bravest person I know (okay, he's not that brave, but that just makes him all the braver, doesn't it?), and about how he has to figure out how to take this totally messed up piece of shit world and fix it so that everyone doesn't die or stab each other, and he can't die in the process (possible wee bit of exaggeration there, but I got really excited to make you excited to read the rest of this. And no these are not author notes by the author, because I am the author, and I am writhing these.)