Original: The Greco-Persian Wars (also often called the Persian Wars) were a series of conflicts between the Achaemenid Empire of Persia and city-states of the Hellenic world that started in 499 BC and lasted until 449 BC.
Simplified: The Greco-Persian wars were a series of wars fought between Ancient Greece and Persia's Achaemenid Empire in the 5th century BC. The struggle lasted 50 years, from 499 - 449.