The Greek War of Independence was a conflict that took place from (1821-1829). The ethnic Greek population, tired of their subjugation under Ottoman rule, decided to band together to reclaim the lands of their ancestors out from foreign rule.
The revolution was organized by a secret society known as the Filiki Eteria, which roughly translates tot he Society of Friends, who's main goal was to overthrow the Ottoman rule and establish a Greek state. Greeks of the time were considered a lower class to their Islamic leadership, and were subject to heavy taxes many bans on ownership for things like Guns and Mounts. Greek-born citizens had to defer in all legal cases to Muslim jurisdiction. Worst of all, Greek citizens were subject to the recruitment of Janissary, where young Greek christian children were conscripted from a young age into the Ottoman army. The Filiki Eteria's goal then, was to reclaim an autonomous state for the Greek people, one where they could live without being second class citizens in their own homes.
The Filiki Eteria were able to gain many allies from people both within and outside the Ottoman Empire, and because of this were able to bolster small scale revolutions in parts around the country. Two of the most notable groups in this process were the Klephts and Armatoloi. These were made up of groups of bandits living in the Ottoman empire who had little ties to either the Greek or Ottoman people, and were made up of free spirits, societal outcasts, and escaped convicts. Those who sided with the Greeks were known as the Klephts, and those who sided with the Ottomans were the Armatoloi. However, alliances within these people were constantly shifting, and it was difficult to know who sided with who. Due to Greece's widespread reputation as the birthplace of Western Civilization, many wealthy American and European aristocrats assisted the Greeks in their revolution. Most notable among them was the famous poet Lord Byron, who assisted in organizing funds and supplies for the Greek revolutionaries, ultimately contracting a fever in 1824 and passing away shortly thereafter. Ultimately however, his death spurred on many more allies in the west until eventually Western powers intervened directly.
Alexander Ypsilantis acted as the leader of the Filiki Eteria in 1821 and began the first rebellions around the Danubian Principalities, gaining support from local Romanian Christians. Ypsilantis would later, however, make some poor judgements in his leadership, leading to him being exiled and eventually dying in poverty. Without him, many small scale revolutions were carried out semi independently all over the Ottoman territories in Greece, where the Sultan was able to get the upper hand. Muhammad Ali Pasha the Great of Egypt was sent by the Ottomans to quell the revolution, and he was very effective at fighting back the Greeks over sea. However, in 1827, the combined fleets of Britain, France, and Russian were able to beat back the power of the Ottoman Empire's naval fleet, thus ensuring Greece would be able to gain it's independence.
The revolution ultimately culminated in the end of the Ottoman empire, as this had marked the first time that a Christian minority had successfully rebelled against the Ottoman empire. The success of the revolution had emboldened other minority groups under the Ottoman flag, such as the Serbs, Bulgars, Romanians, and Arabs. The newly established Greek state, although impoverished from the conflict, was supported by many wealthy allies in Europe, who used their wealth and influence to assist in keeping the country afloat during its early days.
Sources:
https://www.greece.org/march-25th-the-greek-war-of-independence-1821/
https://www.newworldencyclopedia.org/entry/Greek_War_of_Independence