Why did Polybius believe Rome’s expansion required a universal history rather than separate local histories?

Polybius argued that a universal history was necessary because, by 220 BCE, the world’s affairs had ceased to be a series of disconnected transactions and had instead formed an organic whole.12

He believed that Rome’s rapid rise to power had interlinked the affairs of Italy and Africa with those of Greece and Asia, causing all global events to tend toward a single end under Roman domination. Because the actions of these regions were now inextricably tied together, Polybius felt that separate, local histories—which he often criticized as petty or prone to sensationalism—could no longer adequately explain the reality of this new, unified world order.12

To Polybius, the historian’s task was to match this synoptic, organic reality by bringing the operations of the world under one conspectus, thereby providing a comprehensive account of how and why Rome succeeded in subjecting nearly the entire inhabited world to its government within a span of less than 53 years.12