Final answer:
Greece has the Saronic Gulf which geographically separates the Peloponnesus from the region of Attica, with the historic city of Athens located on it. This area was a focal point during the Peloponnesian War, demonstrating the naval strategic importance in antiquity.
Step-by-step explanation:
The country that has the Saronic Gulf separating the Peloponnesus from the region of Attica, with Athens located on it, is Greece. The Saronic Gulf lies to the southeast of the Greek mainland and northwest of the Peloponnesian Peninsula.
Athens, once a powerful city-state, sits on the region of Attica bordering the gulf. The history of this region is marked by significant events such as the Peloponnesian War, where Athens and its allies controlled the coasts and islands of the Aegean Sea, becoming a formidable naval force.
However, Sparta, leading the Peloponnesian League, eventually outmaneuvered the Athenians at sea in crucial battles. This war highlighted the strategic importance of naval power and control over regions such as the Saronic Gulf for ancient Greek city-states.