Herodotus' Histories is fundamentally concerned with the Greek-Persian Wars. In order to accomplish a thorough presentation of these events, Herodotus spends approximately the first half of his work presenting a background for the countries involved and continues this approach in dealing with the events and actors of the wars themselves in the second half. In the first half the background deals with the customs and traditions in the areas which were, or had been, affected by either of the main contenders of the wars (i.e., the Greeks and the Persians). Because of the larger scope of the Persian Empire it consumes a larger portion of the details of background.
In attempting to provide a background for the Persians and the Greeks, Herodotus' assignment has evidently been to present the heritage of these areas. The method of presenting heritage seems to be, in fact, the prime, unifying concept or theme of Herodotus' organizational approach.
The concept of heritage is characteristic of Herodotus' time and it is natural that he should utilize it. That is to say, in the same sense that persons of that time were judged largely on the basis of the merits of their ancestors and their personal lineage, thus it was that countries were to be evaluated on the basis of the forces which played a part in their making - to wit: Because Camyses, son of Cyrus and ruler of Persia, led an expedition against Egypt and because Egypt was not just a small tribe whose heritage could be covered in a paragraph (e.g., the Nasamones; p. 329), a full chapter on Egypt is not out of place. Herodotus found it necessary to present the heritage of Egypt itself in order to show what kind of a people and terrain Cambyses was up against and defeated. Also, the fact that Egypt became a part of the Persian Empire and thus an inherent (if not integrated) element of the Persian heritage makes the heritage of Egypt exceedingly relevant to a consideration of the heritage and composition of Persia. Additionally, Egypt later played a small but key role in the main conflict when it rebelled following the battle of Marathon (Athens vs Persia) and gave Xerxes (of Persia) two battle-fronts just prior to the main battles of the Greek-Persian Wars.
The idea of heritage (of individuals, tribes, or countries) plays a major role throughout The Histories as a means of defining the forces involved in the major Greek-Persian conflict. There are myths, stories and traditions in abundance, providing the substance of most of The Histories and existing in greater preponderance in considering the composition of the Persian Empire than that of the Greeks. This could be the case either because of the greater area and diversity of the Persian Empire, as I have already mentioned, or because, as Herodotus says at one point (I cannot remember or find where, and, thus, what follows is a paraphrase), "it is not my (Herodotus') intention to write about those things which others have already set down."
In addition to the method of background or heritage (or, perhaps, as a means of supplementing it) Herodotus also emphasizes the thematic conflict of democracy versus depotism. In particular, that while the Athenians "were oppressed under a despotic government, they had no better success in war than any of their neighbors, yet, once the yoke was flung off, they proved the finest fighters in the world." (p. 369) Proving, "if proof were needed, how noble a thing freedom is, not in one respect only, but in all." (p. 369)
In approaching any historical work one wants to know to what extent one may trust the writer ... in dealing with Herodotus this raises special questions. In considering the integrity of Herodotus as a historian, two important points should be kept in mind. One is that much of the myths, traditions and considerations of oracles, etc., are not to be seen as factual representations whether Herodotus himself accepts them as such or not. Toward the end of presenting a heritage of the forces involved, which seems to have been Herodotus' focal method, we need not be concerned with Herodotus' opinions, but only with what he reports as having seen or heard. For example: "The storm lasted three days, after which the Magi brought it to an end by sacrificial offerings ... or, of course, it may be that the wind just dropped naturally." (p. 50) We can assume that the wind dropped naturally if it dropped at all, but that the Persians utilized the ploy of the Magi serves further to characterize them or (in this case) to maintain the characterization.
The second point concerns the question of Herodotus' bias and the veracity of his sources. On these questions Herodotus is fairly clear: e.g., "At this point I find myself compelled to express an opinion which I know most people will object to; nevertheless, as I believe it to be true, I will not suppress it." (p. 487) E.g., "Datis ... had a dream. What the dream was is not recorded ..." (p. 430) E.g., "I cannot say for certain ... for the reports are confused ..." (p. 393) E.g .. ..... a man of reputable family, though I do not know the origin of it." (p. 364) E.g., "In this conflict of evidence, you may agree with whichever party you think is telling the truth." (p. 456) Many more examples could be presented, but these are sufficiently representative. On the basis of such comments we may trust that, unless otherwise stated, Herodotus is telling what he believes to be the truth in essence if not in form (e.g., several of the speeches he renders could not possibly be accurate en toto, but in content we may trust that Herodotus is presenting what he has some grounds for believing true.) On the basis of the above comments we may also trust that Herodotus' judgment is reasonable if not always sound.
Whether or not you believe the heritage concept to be a valid method of historical presentation, consider this: Herodotus is easy to read, there is a continuum of interesting details telling you something about the main actors (whether the actors are individuals, countries, or abstract forces; e.g. democracy), and you can glean an idea about the main events with a full idea of how they came to be. All the elements of excellent history are present by virtue of the method of organization. The perspective of heritage is not familiar to modern readers, but toward the end of giving a thorough, historical account, Herodotus has scarcely been improved upon.