Greek War of Independence - Wikipedia

On September 23, 1821, after the fall of Tripolitsa, Greek forces massacre 30,000 Turks during Greek War of Independence. From the article:

"Even several decades before the fall of Constantinople to the Ottoman Empire in 1453, most of Greece had come under Ottoman rule.[5] During this time, there were several revolt attempts by Greeks to gain independence from Ottoman control.[6] In 1814, a secret organization called the Filiki Eteria was founded with the aim of liberating Greece. The Filiki Eteria planned to launch revolts in the Peloponnese, the Danubian Principalities, and in Constantinople and its surrounding areas. By late 1821, the insurrection had been planned for 25 March (Julian Calendar) 1821, on the Feast of the Annunciation for the Orthodox Christians. However, as the plans of Filiki Eteria had been discovered by the Ottoman authorities, the revolutionary action started earlier. The first of these revolts began on 6 March/22 February 1821 in the Danubian Principalities, but it was soon put down by the Ottomans. The events in the north urged the Greeks in the Peloponnese into action and on 17 March 1821, the Maniots declared war on the Ottomans. This declaration was the start of a spring of revolutionary actions from other controlled states against the Ottoman Empire.

On 25 March the revolution was officially declared and by the end of the month, the Peloponnese was in open revolt against the Turks. By October 1821, the Greeks under Theodoros Kolokotronis had captured Tripolitsa. The Peloponnesian revolt was quickly followed by revolts in Crete, Macedonia, and Central Greece, which would soon be suppressed. Meanwhile, the makeshift Greek navy was achieving success against the Ottoman navy in the Aegean Sea and prevented Ottoman reinforcements from arriving by sea.

Tensions soon developed among different Greek factions, leading to two consecutive civil wars. In the meantime, the Ottoman Sultan negotiated with Mehmet Ali of Egypt, who agreed to send his son Ibrahim Pasha to Greece with an army to suppress the revolt in return for territorial gain. Ibrahim landed in the Peloponnese in February 1825 and had immediate success: by the end of 1825, most of the Peloponnese was under Egyptian control, and the city of Missolonghi fell in April 1826 after a year-long siege by the Turks. Although Ibrahim was defeated in Mani, he had succeeded in suppressing most of the revolt in the Peloponnese, and Athens had been retaken.

Following years of negotiation, three Great Powers—Russia, Britain and France—decided to intervene in the conflict and each nation sent a navy to Greece. Following news that combined Ottoman–Egyptian fleets were going to attack the Greek island of Hydra, the allied fleet intercepted the Ottoman–Egyptian fleet at Navarino. The battle began after a tense week-long standoff, ending in the destruction of the Ottoman–Egyptian fleet. By 1828 the Egyptian army withdrew under pressure of a French expeditionary force to which the Ottoman garrisons in the Peloponnese then surrendered, while the Greeks proceeded to the Ottoman-controlled part of central Greece. After eight years of war, Greece was finally recognized as an independent, sovereign state under the London Protocol of February 1830. Later, in 1832, the London Conference and the Treaty of Constantinople defined the final borders of the new state and established prince Otto of Bavaria as the first king of Greece.

The Greek Revolution is celebrated by the modern Greek state as a national day on 25 March."