The modern Greek state was the a direct result of the revolution of 1821. The newly established state was recognized for the first time by the Great Powers in February 1830 through the London Protocol. Two years later, in 1832, a new treaty recognized Greece as an "independent monarchical state", "under the rule of Prince Otho of Bavaria with the three Courts as guarantors". During the same year the borders of the Greek state were first established, and were defined in the north by the line Amvrakikos-Spercheios.

In 1863, after many years of negotiations and by a unanimous resolution of the Ionian Parliament, the Treaty of London recognized the annexation of the Ionian Islands to Greece. Indeed, on 3 August 1864 the representatives of the Ionian Islands participated in an extraordinary session of the National Assembly.

In 1881, after the resurgence of war in the Balkans and after constant diplomatic negotiations, the greater part of Thessaly and the area of Arta were annexed to the Greek state.

The Balkan Wars (1912-13) established the borders of the Balkan states and the Ottoman Empire. The new treaties expanded the Greek territory and established the annexation of Epirus, Macedonia, the Eastern Aegean islands, and Crete.

After the end of World War I, in 1919 with the treaty of Neuilly, Western Thrace was also annexed.

The present borders of the Greek state were defined in 1947, after the end of World War II, with the annexation of the Dodecanese.