In between the First and Second Punic Wars, the Carthaginians, under Hannibal were building an empire in Spain (also know as New Carthage). Eventually this buildup came into direct conflict with the Roman Empire. The Second Punic War started when Hannibal besieged the city of Saguntum -- Rome had promised to protect the city from attack. The Romans demanded that Hannibal call off the siege and when he refused the Romans declared war. Hannibal invaded central and southern Italy (marching via Spain and the Alps) and won decisive victories at Lake Trasimene and Cannae. However, he wasn't able to completely conquer Rome and ended up retreating to Carthage where the Romans counter-attacked at the Battle of Zama. Roman victory brought the war to an end.