Complex sentence: Before the Punic Wars changed completely the nature of commerce in the Mediterranean, the Roman republic had important commercial exchanges with Carthage, entering into several commercial and political agreements in addition to engaging in simple retail trading.
Split into simpler sentences: Before the Punic Wars completely changed the nature of commerce in the Mediterranean, the Roman republic had important commercial exchanges with Carthage. It entered into several commercial and political agreements with its rival city in addition to engaging in simple retail trading.