Final answer:
Charlie entered the Apennine Peninsula after crossing the Alps and heading south, which primarily includes the country of Italy in Southern Europe.
Step-by-step explanation:
After Charlie passed through the Alps and headed south, he entered the Apennine Peninsula. This area, known as the Apennine Peninsula, is located in Southern Europe and consists primarily of the country of Italy. Southern Europe is characterized by the Apennine mountain range that runs through the entire length of the peninsula and gives the region its name. This is indicated by the historical and geographic context, where the Allies, during World War II, targeted Italy as part of their campaign to liberate Europe from Axis powers, described in the reference which details the amphibious assault of Italy that began on the southern shores of Sicily and proceeded up the peninsula.