Megale Idea implies the goal of reestablishing a Greek state as it was before the invasion of turks from Moggolia, in 12th century. As ancient geographer Stravon wrote, greek world extended west from Sicily, to Mikra Asia and Euxenus Pontus to the east, and from Macedonia and Epirus, north, to Crete and Cyprus to the south. Still in those territories lived greek populations in the beginning of 20th century.
The dream of every Greek always had been to liberate all the territories who were under barbarian yoke, and establish a new state with Constantinople as its capital, as it had been in medieval times. After the achievement of Greek independence in 1821, the Megale Idea played a major role in Greek politics. Between two-thirds and three-quarters of the Greek people remained outside the borders of the limited Greece permitted by the Great Powers, who had no intention that a large Greek state should replace the Ottoman Empire.
Was the concept of liberating lands which belonged for 3000 years to Greeks and from which emerged the classical civilization, nationalism? It was as much as it was the desire of French, Belgians and other Europeans to be liberated from Nazis in 1942.
In the period 1912-1922, this dream almost came truth.
Balkan wars 1912-1913
First World War
Naval battles in Aegean Sea
Liberation of Ionian Land (Minor Asia)
Pontian History and Genocide
Destruction of Minor Asia, 1922