Megali Idea in the context of "Venizelism"

The Kingdom of Greece (Greek: Βασίλειον τῆς Ἑλλάδος, romanized: Vasíleion tis Elládos, pronounced [vaˈsili.on tis eˈlaðos]) was the Greek nation-state established in 1832 and was the successor state to the First Hellenic Republic. It was internationally recognised by the Treaty of Constantinople, where Greece also secured its full independence from the Ottoman Empire after nearly four centuries. It remained a Kingdom until 1924, when the Second Hellenic Republic was proclaimed, and from the Republic's collapse in 1935 to its dissolution by the Regime of the Colonels in 1973. A referendum following the regime's collapse in 1974 confirmed the effective dissolution of the monarchy and the creation of the Third Hellenic Republic. For much of its existence, the Kingdom's main ideological goal was the Megali Idea (Greek: Μεγάλη Ιδέα, romanized: Megáli Idéa, lit. 'Great Idea'), which sought to annex lands with predominately Greek populations.

King Otto of the House of Wittelsbach ruled as an absolute monarch from 1835 until the 3 September 1843 Revolution, which transformed Greece into a constitutional monarchy, with the creation of the Prime Minister as head of government, universal male suffrage and a constitution. A popular insurrection deposed Otto in 1862, precipitating the gradual collapse of the early Greek parties (English, French, Russian), which had dominated Greek politics.

Enosis (Greek: Ένωσις, IPA: [ˈenosis], "union") is an irredentist ideology held by various Greek communities living outside Greece that calls for them and the regions that they inhabit to be incorporated into the Greek state. The idea is related to the Megali Idea, a concept of a Greek state that dominated Greek politics following the creation of modern Greece in 1830. The Megali Idea called for the establishment of a larger Greek state including the lands outside Greece that remained under foreign rule following the Greek War of Independence in the 1820s, but which nevertheless still had large Greek populations.

The most widely known example of enosis is the movement within Greek Cypriots for a union of Cyprus with Greece. The idea of enosis in British-ruled Cyprus became associated with the campaign for Cypriot self-determination, especially among the island's Greek Cypriot majority. However, many Turkish Cypriots opposed enosis without taksim, the partitioning of the island between Greek Cypriots and Turkish Cypriots. In 1960, the Republic of Cyprus was born, resulting in neither enosis nor taksim.

Greek nationalism, otherwise referred to as Hellenic nationalism, refers to the nationalism of Greeks and Greek culture. As an ideology, Greek nationalism originated and evolved in classical Greece. In modern times, Greek nationalism became a major political movement beginning in the early 19th century, which culminated in the Greek War of Independence (1821–1829) against the Ottoman Empire.

Greek nationalism became also a potent movement in Greece shortly prior to, and during World War I, when the Greeks, inspired by the Megali Idea, managed to liberate parts of Greece in the Balkan Wars and after World War I, briefly occupied the region of Smyrna before it was retaken by the Turks.

Ioannis Kolettis (Greek: Ἰωάννης Κωλέττης; 1773 or 1774 – 17 September 1847) was a Greek politician who played a significant role in Greek affairs from the Greek War of Independence through the early years of the Greek Kingdom, including as Minister to France and serving twice as Prime Minister. Kolettis is credited with conceiving the Byzantine restorationist and irredentist Megali Idea or "Great Idea" which became the core of Greek foreign policy until the early 20th century.