North Africa and the entire Mediterranean area all the way to the mid east.
Julius Caesar did not establish the ancient Roman empire. He did help expand the territory that ancient Rome had conquered. Many historians have said that the beginnings of Rome as an empire came with the final defeat of Carthage. This gave Rome control over a vast area in the western Mediterranean Sea.
It was located in today's Tunisia. It established a great trading empire which gave it the resources to maintain a strong fleet and army.
Sicily .
The Carthaginians were Phoenicians, and this initially gave them a base in the Western Mediterranean Sea. When Carthage increased its coverage over the whole area, it provided a source of goods flowing west and a market outlet going west.
Three results of the Punic wars were: 1) the elimination of Carthage as a rival to Rome by destroying the city, 2) Rome gained territory in Spain, Sicily, North Africa and all other places that Carthage had colonies, and 3) Rome controlled the entire Mediterranean area.
The Island of Sicily , North Africa and the western Mediterranean sea .
Carthage.
Carthage's attack on Sargentum in Spain gave Rome the excuse to declare war on Carthage as a breach of the Ebro-line treaty.
It gave him the opportunity to intervene on the side of Carthage and seize territory in the Adriatic while Rome was tied up in the west. Of course this gave the Romans the excuse to attack and loot Macedonia after it had defeated Carthage.
Th effects of the rivalry between Carthage and Rome for trade control in the Mediterranean was three wars with Rome being victorious in all of them. After the second of the wars Rome effectively controlled the entire western Mediterranean.
Cato the Elder.