Answer: Republicanism
The Roman Republic was responsible for the conquering and occupation of these territories. Afterwards the Roman Empire was much much larger its territories included Italy, Vatican, San Marino, Andorra, Malta, Cyprus, Greece, Macedonia, Serbia and Montenegro, Croatia, Slovenia, Albania, Bulgaria, Spain, Portugal, Liechtenstein, Switzerland, Belgium, France, Monaco , The whole of Luxembourg, most of Austria, Bosnia and Herzegovina, Hungary, Germany, Romania, the United Kingdom, the Netherlands,
Lebanon, Syria, Israel, Palestine, Turkey, most of Jordan
across Tunisia, Egypt, Libya, Morocco.
Spain,Greece and Gaul were more notably conquered during the republic,this should be your answer.
