The London Protocol 3 February 1830 was an agreement between the three Great Powers (The United Kingdom of Great Britain and Ireland, The Kingdom of France and the Russian Empire), to recognise Greece as an independent, sovereign state.
As a result of the Greek War of Independence, which had begun in 1821, and the Great Powers’ intervention in the conflict in the Battle of Navarino (1827), the creation of some form of the Greek state in southern Greece had become certain. In 1827, the Greek Third National Assembly entrusted the governance of the fledgling nation to Ioannis Kapodistrias, who arrived in Greece in January 1828. Alongside his efforts to lay the foundations for a modern state, Kapodistrias undertook negotiations with the Great Powers as to the extent and constitutional status of the new Greek state.
In March 1829, the foreign ministers of the Great Powers signed the first London Protocol, according to which Greece would become an autonomous, tributary state under Ottoman suzerainty, under an elected Christian prince and encompassing the heartlands of the Greek uprising, the Morea (Peloponnese), Continental Greece and the Cyclades.
Kapodistrias’ diplomatic manoeuvres, aided by the Russian victory in the Russo-Turkish War of 1828–29, resulted in a revision of the protocol on 3 February 1830. According to it, Greece would be fully independent of the Ottoman Empire, but its borders were reduced to the Aspropotamos–Spercheios line.
The Aspropotamos–Spercheios line or Achelöos–Spercheios line (Greek: Γραμμή Ασπροποτάμου/Αχελώου – Σπερχειού) was Greece’s first land border with the Ottoman Empire.
It would start at the mouth of the Achelous River (then known as “Aspropotamos”), pass through Artotina along the ridge of Mount Oeta and reach the Malian Gulf at the mouth of the Spercheios River, passing south of the city of Zitouni (modern Lamia), which would remain in Ottoman hands. The island of Euboea (Negroponte), the Northern Sporades, Skyros, and the Cyclades including the island of Amorgos would become part of Greece
Leopold of Saxe-Coburg (the future King of Belgium) was selected as the first King of Greece, but he rejected the offer.
The protocol was yet again amended in the London Conference of 1832, which established the final borders of the Kingdom of Greece and gave the crown to the Bavarian prince Otto.