(The following work represents the views and opinions of the author, and should not be regarded as part of the Doctor Who canon.)
Other authors have on occasion attempted to write the history of the Daleks, but often the results have been unsatisfactory or inconsistent with one or more known facts. The reason for this is presumably related to the Daleks' use of time travel.
It is clear from observing the travels of the Doctor that there is more to time travel than simply travelling in time. Many races have (or will) develop or acquire time travel technology, yet their ability to use this technology is often limited in various ways. Attempting to use time travel to alter history in any significant way can have dire consequences (see “Father’s Day”, 2005), and yet it is clearly not impossible (see just about every other Doctor Who adventure). The obvious conclusion is that there are at least two different levels of time-travelling/manipulating ability. Most races only progress to the first level, which will be referred to as ‘simple time travel’ and which allows them to move about in time and make observations and minor changes. However there are a few races that develop a much deeper understanding of time, which brings with it a much greater ability to travel in and change history: this will be referred to as ‘sophisticated time travel’. The Time Lords are the most obvious example of the latter, and are presumably the race that developed the greatest understanding and ability of all.
This raises the question of what level of time travel ability the Daleks possess. It is clear that at some point in their history the Daleks developed or otherwise acquired simple time travel, but they clearly recognised its limitations and didn't try to storm the past with vast fleets of timeships. Rather, they attempted subtle and covert changes to history (for an example see “The Evil of the Daleks”, 1967).
However at some point the Daleks developed sophisticated time travel, although presumably never to quite the same level as the Time Lords, and once at this level they were able to interfere with history in much more significant way. A key point to realise is that they would have been able to interfere with their own history to an extent unimaginable by less developed races: this means they would have become effectively immune to attacks on their own past.
For example, suppose they had been attacked and wiped out shortly after their creation. For most races this would mean extinction, but future Daleks could travel back in time and create a new origin for themselves. Indeed, they could have planted genetic and cultural seeds of their own existence in many races so as to ensure they would never die out (for early evidence of such intent, see again “The Evil of the Daleks”). Our elementary notions of cause and effect suggest that this should be paradoxical and impossible, but this is in a sense what distinguishes a simple (or non) time traveller from a sophisticated one: just because we don't understand how it would be possible doesn't mean the Daleks couldn't do it.
At this point, ‘Dalek history’ would cease to have any real meaning. They could have multiple contradictory origins, they could be wiped out time and again and yet still exist, their appearance and technical abilities could change apparently at random, and so on. They would cease to be an ordinary race and become instead a sort of a universal bogey-man. This is not to say that the Universe would always be teeming with Daleks however; sometimes there might be hordes of them, at other times only a few, and at other times none at all. But there would always be memories of them and the potential for them to exist again; if you hang around in any one place long enough a Dalek is pretty much guaranteed to come along and exterminate you.
The only way to destroy such a race would be to wipe them out of existence at all points in time and space, in a ‘time war’. Such a war was eventually fought between the Daleks and the Time Lords.
The time war went largely unnoticed by most races, presumably because much of it was fought in times and places that were beyond the span of their histories, or were lost in time-lines that were unrealised from their point of view. Collateral damage could have resulted in entire civilisations being wiped out, but only races that had developed sophisticated time travel would have noticed, since it would have been as if the civilisations had never existed in the first place. In the event, the time war was unsuccessful, as a number of Daleks survived in some nook or cranny of the time-space continuum. From there it was only a matter of time (no pun intended) before they emerged once again.
As an aside, I noted that future Daleks could have planted genetic and cultural seeds in the past to ensure their own existence. One could take this idea further and speculate that they may have actually created progenitor races rather than just modified them. Since all Dalek origin stories have them developing from human or humanoid ancestors this could explain why the humanoid form is so common in the Universe, and would also mean we owe our own existence to the Daleks.
John Rocco Roberto has given us a remarkably detailed discussion of Dalek history and the Time War in his essay The History of the Time War. Check it out.