The Histories is exactly what it purports to be—it's a history text explaining who the important figures were in human history, what their effects were on each other, who won which wars, and what the real reason was behind those wars. Herodotus is not exactly an unbiased narrator, but his bias is easy to spot; here's a huge hint—he tends to depict Greek history with more honor and class, and he tends to depict their enemies as especially capricious and violent.
Although the story is beautiful told, with all sorts of people groups and many, many kings and cultures, the stories to eventually solidify into one cohesive account of the Histories' most important conflict, the conflict between Persia and Greece. Essentially, what the reader will learn if they are disciplined enough to follow the story along through to its completion is that Greece was not nearly as coordinated or unified before their war against Darius and Xerxes, his successor.
That doesn't mean that Greece is suddenly nationalized or something, and there are many more wars to be had in Greece, most famously, the Trojan War. But, it does mean that Greece can now operate more as a nation in the broader political landscape. In other words, they are less likely to be attacked by invaders since everyone knows that they worked together to defeat the Persians.
Herodotus himself maintains that the true value of the story can be found in the glory of the individual souls who died on the battlefields. He encourages us to look on this history as our shared human history so we can pay our respects to those who have come before us. That is something the reader should decide for themselves, how they will relate to the book, but without question The Histories brought a better kind of history to the West, and we do owe Herodotus thanks for that.
