The correct answer is A) military conquest.
The factors that contributed most to the expansion of both the Persian and the Greek Empire were military conquest.
The Greeks and the Persian Empire had powerful armies. In the case of the Greeks, the Athenians had a fantastic navy that was used to conquer other nations. Let's remember that Athens had many city-states that were controlled by the power of Athens. One example of great conquest was the powerful empire under Alexander the Great, who conquered many territories in Asia and Africa. The Persians also were a powerful Empire. They conquered big portions of the Middle East lands and fought battles with Greek armies such as the Spartans.
