There is only so much complication that the human mind can comprehend; once complexity reaches a certain level, one that is different for each person, the ability to perceive the interplay amongst each component disappears. In books, movies and TV shows, this results in a limited number of main protagonists and antagonists. If the scope is not contained, then the story feels disjointed and convoluted to the audience.
The same is true in the study of history and in particular ancient history. Rome is a simple example; there is Rome and the “others.” The intricacies of the Roman state may be infinitely complicated, deep and full of characters pulling for one agenda or another, but when it comes to identifying a period as a historical one that can be covered in a continuous narrative, Rome is the ultimate. In fact, Rome is so much of a historical era that it is written in three or more eras: the republic, the empire and the fall. Of course each of those eras can be further broken down into smaller narratives, but such is always the case.
The nature of “Greece” makes even this level of narrative more difficult as nearly every city was a polis and each polis was an autonomous state. This has not stopped historians from covering the so-called Golden Age as a historical narrative, but they tend to actually be covering Athens and Sparta, with other city states such as Corinth, Thebes and Megara appearing as side, rather than main, characters. There is some justification for this decision, largely resting in the dearth of information from most Greek city states and the undeniable preeminence of Athens and Sparta. This said, it is still an artificial creation.
This brief introduction in the creation of historical periods and narratives leads up to the Hellenistic Age, called because it saw the spread of Greek-ish (as Hellenistic implies) culture throughout the Eastern Mediterranean and parts of Asia. Loosely this period is defined from Alexander’s death until the advent of Rome, but when precisely it ends it difficult to say. This seems a solid block of time that could well be considered for a narrative, yet almost every historical book on the age covers three narratives, one-third of the whole narrative or only covers it in topical format. My proposition is that this stems from there being three main Hellenistic Kingdoms, each with their own peculiarities and issues. Then there are the Greek city states and two further Kingdom’s of sorts, one the Attalid state in Pergamum and the other the city state of Syracuse. All in all, the Hellenistic age is complex, but even with several thorough books on many of these issues, most scholarship and writing is set on avoiding the other end of the spectrum, which is to say that all three Hellenistic kingdoms were the same and therefore can be painted with one brush.