Answer and Explanation:
they had to themselves against Achaemenid Persians, they had to adapt new tactics of warfare, advance their warships and improve the equipment of soldiers. One of the major progresses of Greece during the first Perso-Greek war was adaptation of Bronze shields and bronze weaponry. Since Persians were always superior in numbers, they could send large armies to invade greek states. Therefor making numerous advances. It also helped them become closer.
