Polybius, a Greek from the Achaean league in southern Greece, wrote The Histories to show how Rome rose to dominate the Mediterranean. This is Book 4. Book 3 left Hannibal, the Carthaginian general, in Italy after he crossed the Alps and destroyed Roman armies at Trebia, Trasimene, and Cannae; the Republic — Rome run by a senate and elected officials, not a king — still held.

While Hannibal is still in Italy, Polybius turns to Greece in 220 BC. The Social War is a smaller ruin. The Aetolians and the Achaeans, the two federal leagues of European Greece, tear at each other. Philip V of Macedon is still a young king. Dorimachus and Scopas raid. Cynaetha is sacked after faction has already eaten the city. Byzantium taxes Black Sea grain and makes enemies of Rhodes. Philip learns raid and counter-raid in the Peloponnese, the southern peninsula of Greece. Polybius, an Achaean, writes with his own league on the table.