Which earlier events did Polybius cover in the introduction to the Histories?

In the introduction to his work, The Histories, Polybius included an account of Roman history beginning in 264 BCE, when Rome first crossed into Sicily to engage the Carthaginians.1

These introductory books (Books I–II) also cover significant events occurring in other parts of the world, with a particular focus on Achaea, during the period between 264 and 220 BCE. While Polybius originally intended for his main narrative to begin in 220 BCE—the year he believed marked the start of events he could document through direct witness testimony rather than "hearsay at one remove"—these earlier chapters were essential for providing the necessary historical context for Rome's rise to global supremacy.12