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Operation Yukthiya
Operation Yukthiya (Sinhala for 'justice') is Sri Lanka's anti-drug crackdown launched 17 December 2023 by Acting IGP Deshabandu Tennekoon and Minister Tiran Alles, with over 100,000 arrests by May 2024 and UN-documented torture and arbitrary detention allegations.
Operation Zarb-e-Azb
Operation Zarb-e-Azb, also known as the North Waziristan offensive, was a joint Pakistan Armed Forces operation launched on 15 June 2014 against militants in North Waziristan.
Operativo Independencia
Operativo Independencia was an Argentine military operation launched in Tucumán in February 1975 under Decree 261/75, ordering the armed forces to annihilate militants, and marking the start of clandestine repression.
Opium Wars (鸦片战争)
The Opium Wars (鸦片战争) were two 19th-century wars, 1839–1842 and 1856–1860, in which Britain, later joined by France, defeated Qing China over the illegal opium trade, producing unequal treaties, the cession of Hong Kong, treaty ports, and the legalization of opium.
Opposition to World War I
Opposition to World War I: religious, political, and labor resistance to the 1914-1918 war, including conscientious objection under conscription in Britain, New Zealand, and the US, socialist and women's antiwar activism, and wartime repression under the Espionage and Sedition Acts.
Oradour-sur-Glane massacre
Oradour-sur-Glane massacre: 10 June 1944 killing of 642 villagers by the Waffen-SS Division Das Reich's Der Führer regiment, men shot in barns, women and children burned in the church; ruins kept as a French national memorial.
Oran massacre of 1962
The Oran massacre of 1962 was the killing of several hundred European residents of Oran, Algeria, on 5 July 1962, the day Algerian independence was celebrated.
Orange County Men's Central Jail escape
January 22, 2016 jailbreak from the Central Men's Jail in Santa Ana, California, by Hossein Nayeri, Bac Duong, and Jonathan Tieu, who cut through plumbing tunnels, rappelled from the roof, and were recaptured after eight days.
Order No. 227 'Not One Step Back'
Order No. 227 'Not One Step Back' was a 1942 order by Joseph Stalin banning unauthorized retreat in the Red Army and creating penal units.
Örebro school shooting
Örebro school shooting, Campus Risbergska, Sweden's worst mass shooting: on 4 February 2025 Rickard Andersson, 35, killed ten people at an adult education center before taking his own life; investigation closed with no ideological motive.
Organisation armée secrète
Organisation armée secrète (OAS), French clandestine terrorist organization founded in early 1961 by Lagaillarde, Susini, and generals Salan and Jouhaud to oppose Algerian independence; waged bombing campaigns in Algeria and France, 1961–1962.
Organisation Todt
Organisation Todt (Todt Organization) was the civil and military engineering and construction organization of Nazi Germany, created in May 1938 and named after its founder Fritz Todt.
Origins of the Six-Day War
Origins of the Six-Day War: how the 1948 armistice lines, the Jordan River water dispute, Syrian border clashes, and the May 1967 crisis, including the UNEF withdrawal and Straits of Tiran blockade, led to the June 5-10, 1967 war.
Orio Palmer
Orio Joseph Palmer (1956-2001) was an FDNY battalion chief who climbed to the 78th floor South Tower impact zone on 9/11, radioing conditions; his recovered 2005-released transmissions revealed the highest FDNY ascent that day.
Orlando nightclub shooting
June 12, 2016 mass shooting and terrorist attack at Pulse, a gay nightclub in Orlando, Florida; 49 killed, 53 wounded; shooter pledged allegiance to ISIS in a 911 call and was killed by police after a roughly three-hour standoff.
Orlov revolt
The Orlov revolt (Greek: Ορλωφικά) was a 1770 Greek uprising against Ottoman rule in the Peloponnese, instigated and aided by Russia and named after the Orlov brothers.
Osage Indian murders
The Osage Indian murders, or Reign of Terror, were early-1920s killings of oil-wealthy Osage Nation members in Oklahoma for their headrights, culminating in William K. Hale's 1929 conviction in the FBI-forming federal investigation.
Osaka Incident
The Osaka Incident (大阪事件, Ōsaka jiken) was a failed 1885 plot by Ōi Kentarō's Liberal Party left wing to send armed activists to Korea and install the pro-Japanese Independence Party.
Osama bin Laden death conspiracy theories
Osama bin Laden death conspiracy theories claim the al-Qaeda leader killed in the May 2, 2011 Abbottabad raid survived or that the operation was staged; fact-checkers, DNA evidence, al-Qaeda's own statement, and declassified documents refute them.
Oscar López Rivera
Oscar López Rivera (born 1943, San Sebastián, Puerto Rico), FALN member convicted of seditious conspiracy in 1981, served almost 36 years in US prisons before Obama's January 2017 commutation; released May 17, 2017; diagnosed with Alzheimer's in 2024.
Oskar Gröning
Oskar Gröning, the Bookkeeper of Auschwitz (Buchhalter von Auschwitz), an SS-Unterscharführer at Auschwitz-Birkenau 1942–44, convicted in 2015 of accessory to murder in 300,000 cases and sentenced to four years, confirmed by the BGH in 2016; he died 9 March 2018 at 96 without serving the sentence.
Oskar Schindler's Enamel Factory
Oskar Schindler's Enamel Factory (Fabryka Emalia, Deutsche Emailwarenfabrik) in Kraków's Zabłocie district: wartime factory where Schindler employed Jewish forced laborers, now a Museum of Krakow branch opened 2010 about occupied Kraków 1939–1945.
Otley Run pub crawl attack
Otley Run pub crawl attack: 26 April 2025 crossbow and firearm attack on Otley Road, Headingley, Leeds, by Owen Lawrence, 38, who wounded two women before dying of a self-inflicted airgun injury two days later; he left a misogynistic far-right manifesto.
Ōtomo–Shimazu conflict
The Ōtomo–Shimazu conflict was a series of Sengoku-period wars in Kyushu between the Ōtomo and Shimazu clans, culminating in the Shimazu victory at Mimikawa in 1578.
Otto Ohlendorf
Otto Ohlendorf (1907-1951), German SS-Gruppenführer and lawyer-economist, headed RSHA Amt III (SD-Inland) and commanded Einsatzgruppe D, responsible for about 90,000 killings; chief defendant in the 1947-1948 Einsatzgruppen Trial, executed at Landsberg in 1951.
Ottoman capture of Béjaïa
The Ottoman capture of Béjaïa, or Capture of Bougie, took place in September 1555, when Salah Rais, ruler of Algiers, took the fortified port city from its Spanish garrison.
Ottoman conquest of Algeria
The Ottoman conquest of Algeria brought the central Maghreb under Ottoman sovereignty between 1516 and 1519, when the Barbarossa brothers fought Spanish forces on the Algerian coast.
Ottoman conquest of Epirus
The Ottoman conquest of Epirus (1430–1479) absorbed the late Byzantine Despotate of Epirus into the Ottoman Empire, beginning with Ioannina's negotiated surrender to Murad II.
Ottoman conquest of Hungary
The Ottoman conquest of Hungary (1521–1541) was Suleiman I's destruction of the medieval Kingdom of Hungary at Mohács in 1526 and annexation of Buda in 1541.
Ottoman Empire in World War I
Ottoman Empire in World War I: the Ottoman state as a Central Powers belligerent, 1914-1918, fighting at Gallipoli, in the Caucasus, Mesopotamia, and Palestine, ending with the Mudros armistice and the empire's disintegration.