Complex sentence: Hannibal marched north to Venefram, which caused alarm in Rome that it was his objective, then the Carthaginian army suddenly turned east into Samnium, and finally Hannibal crossed the Apenine Mountains, and moving via the Pelignial plains, entered Apulia.
Split into simpler sentences: Hannibal marched north to Venefram, which caused alarm in Rome as was his objective. Then the Carthaginian army suddenly turned east into Samnium, and finally Hannibal crossed the Apenine Mountains, and moving via the Pelignial plains, entered Apulia.