A mountain is a mountain because it wants to be, and that's the best way I know to explain it.
My father raised me in a cottage outside Anvilmar. He refused to settle in the Bronzebeards' underground city. Not just because living closer to the wilderness brought him closer to game. Not just because we were considered somehow tainted because somewhere back before most dwarves were alive to remember, a Dark Iron claimed our last name. My father didn't trust Ironforge. Not the politicians or the guards, he didn't trust the very idea of a city carved out of a mountain. He often mused about how the dwarves felt living where they did made them safe, while all it would take was a good earthquake and half the dwarven race would be smothered within seconds. It was rare for me to see the city as a child. It was only with unrelenting begging that I won the occasional trip, and usually it was because my father needed something there anyway. Most times, though, I didn't get to go. And he would tell me, "Buundhil, lad, a mountain is a mountain because it wants to be a mountain. It don't want to be no damn city."
And that, I guess, is why the world needs the Thousand Wardens. No matter how many fancy gagdets the gnomes and the goblins conjure up, no matter how many guns we got or cities we build, people will always be at the mercy of what them tauren call the Earth Mother. And there's got to be someone who can keep us from abusing nature, while protecting our people from the kind of world where you're predator or prey and right and wrong got nothing to do with it. The Wardens are here to guide you through the forest when no one else can, and to make sure it don't burn.
There's a lot we don't know about how the Wardens began. We're pretty sure the first Wardens gathered some time after the earthen came up out of the deep places of the world and became the dwarves. We know their purpose was to guide folk through the wilderness, and to guard young settlements from wild animals and the like. We know they were trappers, hunters, explorers, cartographers, minstrels, storytellers, and troubadours. Eventually, their numbers grew to a point where they wanted some kind of way to communicate with each other, so some of the magic users among them created the first Wardens Runestones. The stones let Wardens speak with each other over great distances as well as letting them locate where other Wardens could be found.
There are a lot of questions about who exactly, race-wise was in the original Wardens. We know there were dwarves, humans, tauren, and high elves. Probably night elves too, but no one's sure how they were in the Wardens and managed to keep their race secret until the Third War. My guess is back then most folk didn't know a high elf from a night elf from a hole in the ground. There were probably trolls. Don't know about gnomes. They were around, I know that, but they kept to themselves and most folk didn't know about them until just before the First War. Not to mention they aren't exactly lovers of nature.
It were the First War that saw the end of the original Wardens. Aye, and the Second and the Third. Wardens found themselves on different sides of the battlefield, and most wouldn't survive. Too many were risen as mindless, undead drones of the Lich King. Most of those who did survive with their souls intact cast aside their identity as Wardens, ashamed of raising their hands against brothers and sisters. Since few outside its ranks were even aware of its existence to begin with, the Thousand Wardens just faded away.
That is, until Grimthur Oakreaver revived the group upon the re-opening of the Dark Portal. With the Burning Legion renewing its attacks on Azeroth, Oakreaver gathered a new, smaller group of heroes. Myself included, you know. Never met Oakreaver myself but I hear he were a nice enough fellow. He disappeared not long after the Wardens returned, and was found frozen in a block of ice in the basement of an ancient Wardens fortress - Angmar in the Badlands. To date, no one knows what happened to poor Grimthur.
Smaller in number, no longer restricted to just wilderness folk, the new Thousand Wardens crossed the Threshold to broken Draenor and helped stem the tide of the Burning Legion. The Wardens fought for the safety of Azeroth and its people until shortly after the traitor Arthas renewed his assault on the free people of the world. Apparently somehow threatened by our meager numbers, Arthas targeted the Wardens for extermination. Our fortress in the Badlands was destroyed. Assassins were sent after Wardens members. Regrettably, but necessarily, we went into hiding. Our good friends in the organization known as Veritas sheltered many of us for a time.
It is just in the past few weeks that the Wardens have returned to continue our work defending Azeroth. Old members have been found in every corner of the three continents. At the same time, we are receiving word that the Wardens of the Horde have also returned. Our communication with them is necessarily (and as far as I'm concerned, garetfully) limited, but from what we hear, their numbers grow every day.