In 1587, the English founded a colony at Roanoke Island, in Virginia. Three years later, only ruins remained. All 117 settlers were gone.
As everyone knows, this didn't stop the English from colonizing North America. Twenty years later, in 1607, they founded Jamestown, and while that colony struggled at first, with the majority of its settlers dying in the hard winter of 1609-1610 until only 60 lived, Jamestown survived and the rest is history.
These early colonies were founded in the recent wake of the Dark Ages, from about 532 A.D. when Rome fell to barbarian invaders, to the early 1500s when the Renaissance took hold. The thousand years in between mark one the longest periods of times in history when people, in this case in Europe, were living in the shadow of an earlier, more advanced civilization than their own. By the Renaissance, technology and social organization were moving forward again to historic new heights.
Progress is like that. It suffers setbacks, but is rarely entirely defeated. When conditions are right, a false step may doom those immediately involved, but rarely prevents someone else from going forward.
In the same vein, when progress gets ahead of itself, it often stalls. Consider the Apollo program. Man set foot on the moon in 1970. Yet, a few missions later, the program was ended, and a generation later, in 2006, we have President Bush making a long term program to return to the moon a priority for NASA.
This wouldn't be the first case of premature progress stalling. The math of chaos and fractals languished in obscure Russian mathematics journals for two generations until researchers aided by computers were able to pick up the ball and move forward again. Fermat's Theorem remained unproven for centuries, until advances in seemingly unrelated areas of mathematics made it possible for scientists to pick up the ball and prove, probably far more crudely than Fermat did, that his theorem was indeed true.
A recurring theme in science fiction is that of a civilization living, as the Europeans of the Dark Ages did, in the shadow of a great prior civilization. Sometimes the prior civilization is alien -- much of Larry Niven's writing and the science fiction writing of Kate Elliot, for example, use the device. At other times, the setting is post-apocalyptic.
Almost everyone in the scientific community agrees that this isn't the situation today. Life on Earth evolved on Earth with no alien assistance (or if you want to be really far fetched, but morally equivalent, with the help of primitive spores that arrived on Earth after floating for millions of years through empty space, several billions of years ago, and life evolved from there).
Likewise, there is strong evidence from numerous sources like archeology, genetics, and linguistics, that corroborate a history in which technology and social organization have never been as advanced as they are today, and that this has been the case for several hundred years, at least. Realistically, humanity has been setting new records of achievement technologically and in terms of social organization, and breaking new ground, continually since around the Renaissance.
Indeed, globally speaking, there are solid arguments that much of the dark ages weren't themselves, all that dark, because the Arabic empire, which was in a golden age by the late 600s, remained a center of advancing intellectual progress, building on Roman and Greek knowledge, until the Ottoman Empire took hold in the 1500s or so, fueling an intellectual and social decline in the Middle East that ultimately gave way, first to Western colonialism, and then to the malaise of an intellectually closed society that much of the Islamic world is still struggling to emerge from today. Still, the Byzantines and Islamic empire carried the torch until the Europeans took it up again in the 1500s, so the every moving peak of technology and social organization for humanity as a whole has seen few setbacks.
You probably have to go back until well before the golden ages of the Greeks and before them the Egyptians, several thousand years ago, before you really see extended periods when human progress was set back in all places by the decline of a particular empire.
Still, this chain of progress goes back only so far. Stone tools, wooden spears and fire making date back to before any species that biologists and anthropologists have been willing to call Homo sapiens, around 750,000 years. Neanderthals roamed the Earth starting about 200,000 years ago. Modern humans may be almost as ancient and certainly date back, at least, 100,000 years. This is all a blink in the eye of the 65,000,000 years since dinosaurs were replaced by mammals and birds, and the 4 billion year history of life, and the 14 billion years that have elapsed since the Big Bang, but, most of that isn't really our history.
But, all modern civilization can trace its roots ultimately to the Neolithic revolution of 10,000-12,000 years ago. Since then, there have always been domesticated plants and animals, alcohol, pottery, cloth, and permanent human settlements, all over the world. We don't know for sure who was first, although we can make some educated guesses, but the word spread fast, over continent size regions within a couple of hundred years. By 6,000 years ago, the Sumerians in present day Iraq had a written language, an elaborate religion (some of whose traces survive in the major religions of today through Judaism, at least), sailboats, and copper and bronze tools.
Before then, about 90-95% of our species' history, we were hunter-gatherers, living in small tribes, without agriculture or metal tools.
This is the basic story, and it comes with lots of evidence to back it up. Still, one wonders, were there ancient Roanokes? Were there outbreaks of Neolithic revolution, pre-bronze age class civilization that arose and survived, perhaps for decades, perhaps for centuries, isolated from the rest of humanity by geography somehow, the ultimately sputtered out and died, with the founders of the Neolithic revolution forced to begin anew, without the benefit of their insights? There are dozens of millennia where we know of no reason why this couldn't have happened, and yet we have no evidence that it did. Why? Have we simply not located, or has posterity simply not preserved, evidence of these false starts? Or did they really simply not happen? How would the discovery of some 50,000 year old ancient Roanoke, perhaps in a mountain valley range, or a former Sarahan oasis, or Madagascar, or Australia change our view about who we are as a species?
Were the conditions that gave rise to agriculture and everything that came with it really so unique that hundreds of thousands of tribes in tens of thousands of years were necessary for some tribe to stumble upon it? Did it take a Neolithic Einstein to get our species over the hump? Did a mutation in a critical, but subtle gene, give us the capacity to take this step? Were weather conditions truly remarkable for some brief period? Did some Neolithic ruler bring together enough people in a peaceful alliance that they finally had the critical mass and lack of distractions necessary to invent agriculture, and perhaps also, the need to do so to maintain their little kingdom? Were the false steps so close in time to the actual event, because some event like those just suggested, make the time ripe, that we simply falsely guess now that they have a common source (and that guess, in fairness, isn't universally held).