Greek Independence Day, March 25, is the day the Greeks celebrate the Greek Revolution against the Ottoman Empire. The Ottoman empire ruled over Greece from 1453 until 1832. Prior to this, Greece was ruled by the Byzantine empire.
The war of independence was waged by Greek revolutionaries between 1821 and 1832, after 400 years of occupation and oppression by the Ottoman Turks. With the help of Russia, the United Kingdom, and France, Greece drove the Turks out, and became an independent nation in May 1832.