Final answer:
Polybius begins his narrative in 264 BCE to provide historical context and background for the period of 219-167 BCE, especially to elucidate the significance of the First Punic War and the events leading to the Second Punic War, which were pivotal in the expansion and transformation of the Roman Republic.
Step-by-step explanation:
If Polybius focuses on the period from 219-167 BCE but begins his narrative in 264 BCE, he does so primarily to provide historical context and background for the events he wants to discuss. The inception of the First Punic War at this time marks a significant chapter in Roman history, setting the stage for the rise of the Roman Republic as a dominant power in the Mediterranean. By starting his account at the outset of the Punic Wars, Polybius can offer detailed insight into the causes and repercussions of these conflicts, including the subsequent Second Punic War, and the events that led to the transformation of the Republic. This context is essential to understanding the interplay of military and political developments that characterized Roman expansion and internal struggles, including the class conflicts that triggered reforms and the rise of influential military leaders like Sulla, which eventually culminated in the end of the Republic and the dawn of the Roman Empire.