While the Tanach is not primarily an historical document (it's main focus is clearly legal and moral), it does nevertheless include a great deal of historical information. Over the past couple of centuries, various academic disciplines have launched serious and sustained challenges to the authenticity of this information. In some cases, should the claims prove correct, the Torah itself would (chas v'shalom) be reduced to the status of complete fraud.
Some in the archaeological field have long maintained that the Biblical narrative has been firmly disproved both by reams of directly contrary evidence and by the absence of the corroborating evidence that should have existed but does not. I'm not in any position to offer my opinion on the matter and have neither the time nor the energy to engage in the kind of research curriculum needed to change that.
Fortunately, Professor Kenneth Kitchen, a (retired) Biblical scholar and Egyptologist from the University of Liverpool, is eminently qualified to offer his opinion. And he has. While he certainly doesn't lack his critics, Kitchen, over the past half-century of study, has used his considerable academic weight and impressive knowledge to forcefully contend that the historicity of the entire Tanach is in fact comfortably supported by a vast body of evidence of many types.
In light of Kitchen's efforts, it is no longer possible to casually brush off Biblical events as mere fiction. In other words, while an archaeological layman may not personally be able to reject the accusation of fraud, the accusation itself has now lost its sting.
You might like to read this good review of Kitchen's latest book (On the Reliability of the Old Testament) or a brief summary. And it wouldn't kill you to buy the book itself (or get it from the library).
I should note that the professor himself is not Jewish and thus doesn't share our mesorah. He therefore makes certain assumptions about miracles and the nature of prophecy with which we would strongly disagree. That, however, shouldn't prevent us from benefiting from his key historical positions.
Academic Bible study over the past two hundred years has driven some to the conclusion that the Chumash was written by multiple human contributors. Analysis of text styles, apparent narrative repetitions and variant descriptions of God, have led some to go a step further and declare that Chumash is actually a blend of smaller, distinct documents written over a period of centuries.
This latter approach is popularly known as "documentary hypothesis" ("DH"). As above in our discussion of archeology, if DH's maximal positions were correct, Torah Judaism would simply collapse (as clear claims like that of Devarim 31:24 would be exposed as false).
First of all, let's see if we can't downgrade the threat just a bit. Upon examination, some claims might not actually conflict with our mesorah. For instance, we can agree that not every word of the Chumash was written by Moshe, as one opinion (at the end of Mesechte Makkos) teaches that the final eight verses were written by Yehoshua. We can also agree that there are some disputes over the precise text of the Chumash, as Rabbi Akiva Eiger (commenting on a Tosafos to Shabbos 55b which itself posits multiple textual versions) notes the existence of quite a few words which must have been spelled differently in Rashi's Sefer Torah than in ours (of course, all of these differences are minor and have no effect on halacha).
Next, the core claims of DH. I'm not aware of any significant textual observations made by DH scholars that weren't already known to, and discussed by, classical Torah scholars. The secular scholars' key accomplishment wasn't uncovering new, previously unknown Biblical anomalies, but the rejection (or ignorance) of the already-existing models for resolving them. Our task, therefore, isn't to deny the "problems", but to compare the various models and choose those which are more reasonable.
If you'd like to see a demonstration of my methodology in action, I went into quite a bit more detail in this "ask-the-rabbi" letter from some years back. Take a look.
I will add that, should you choose to read up on this yourself, you will notice that many DH problems only make sense if you assume that prophecy and other miracles are impossible. No support for this assumption is offered, it's just taken as obvious. But that's a classical "tail wagging the dog" error: they conclude that the miracles of the Torah never happened because various passages seem to make no sense...because miracles are impossible!
The Oral Torah
For Orthodox Jews, the Chumash is inseparable from the Oral Law. In fact, without the Oral Law, there would be virtually nothing of substance left about which to be orthodox. Which, in the eyes of a thinking Jew, begs the question: How do we know that God really did transmit an Oral Torah to Moshe?
Loads of material has already been written about this subject so there's really no need for me to write anything new. Here is Rabbi Gil Student's summary of the ways the rishonim approached the problem. And here's my own letter on the subject from a different perspective.
I hope to write more in the near future on the related issue of how we know that our version of the Oral Law is authentic.
Midrashic Material and History
It is not uncommon to read a midrashic account of the deeds or accomplishments of some historical figure or other and wonder how they could possibly have happened. If King So-And-So really had such a massive impact on the world around him or if (literally) earth-shaking events actually took place, why is there no record in any other account of history?
While this isn't the time and place for a detailed discussion, I think it will be enough to observe that midrashim and aggados of Chazal contain some of the most holy, enlightening and startling thoughts available in any literature anywhere. Chazal hid untold treasures within these often strange and obscure passages. But they generally were not meant to be taken literally...they're far too profound for that! Consequently, as a rule of thumb, I would suggest that if you come across a midrashic statement that appears historically problematic, you can rely on the statistical probability that it is among those deeper passages (see the Ben Ish Chai's teshuva - Rav P'alim chelek 1, sha'alah 56 - for an extensive treatment of this subject).