Contemporary
HistoryModernAncient historyArchaeologyContemporaryPost-classicalIndian historyEarly modernAncientHistory by country, small region and cityFrom Lably lessonsHistory by topicHistorical cities, towns and archaeological sitesBasicsPrehistoryHistory by countryHistorical citiesModern historyHistory by subject matterPost-classical historyHistory by continent and large regionAuxiliary historical sciencesHistory & CivicsHistory by subjectHistory by continent and regionHistory by ethnicityHistory by regionGeneral
O
- Occupation of AraucaníaIncorporation of Araucanía into Chile
- Occupation of Czechoslovakia (1938–1945)Period of Czechoslovak history
- Occupation of Iraq (2003–2011)Aspect of the Iraq War
- Occupation of JapanPost-World War II occupation of Japan
- Occupy movement2011–2012 protests against socioeconomic inequality
- October 7 attacks2023 armed incursions and massacres in Israel
- Official Residence of the President (Republic of China)The official residence of the president (Chinese: 總統官邸; pinyin: Zǒngtǒng Guāndǐ; Pe̍h-ōe-j
- Ogaden War1977–1978 war between Ethiopia and Somalia over Ogaden region
- Oil theft in NigeriaOil theft in Nigeria is considered to be the illegal appropriation of crude or refined oil
- Oklahoma City bombing1995 domestic terrorism bombing in Oklahoma City
- Oluseyi PetinrinOluseyi Petinrin (born 19 January 1955) is a retired air chief marshal in the Nigerian Air
- On Contradiction1937 essay by Mao Zedong
- On Guerrilla Warfare (Mao Zedong book)1937 book by Mao Zedong
- On New Democracy1940 essay by Mao Zedong
- On Protracted WarWork of compiled speeches by Mao Zedong
- On Revolution1963 philosophy book by Hannah Arendt
- On the Correct Handling of Contradictions Among the People1957 essay by Mao Zedong
- One America InitiativeOne America in the 21st Century: The President's Initiative on Race , or the One America I
- One country, two systemsChinese constitutional principle
- Open governmentPractice of sharing state documents and proceedings publicly and reusably
- Operacion FenixOperación Fénix (English: Operation Phoenix), was an attack by the Colombian military agai
- Operation AtlantaOperation Atlanta was a road security operation in Đồng Nai Province carried out by the 11
- Operation Atlas WedgeOperation Atlas Wedge was a joint U.S. Army and Army of the Republic of Vietnam (ARVN) mil
- Operation Avalanche (Afghanistan)Operation Avalanche was a four-week U.S.-led aggression in December 2003 designed to disru
- Operation BaawarOperation Baawar (Pashto for assurance), was a major Afghan-led offensive in Afghanistan w
- Operation Badger ToothOperation Badger Tooth was a search and destroy mission in the Street Without Joy area of
- Operation Baikal-791979–80 Soviet intervention in Afghanistan
- Operation BakerOperation Baker was a security operation during the Vietnam War conducted by the U.S. 3rd
- Operation BannerOperation Banner was the operational name for the British Armed Forces' operation in North
- Operation Bedrock (Laos)Operation Bedrock (Laos) (1–9 November 1971) was a military offensive staged by the Royal
- Operation BeninCotonouCotonou (Benin)
- Operation Big BirdAttempt by the Philippine government to recover stolen money
- Operation BillingsOperation Billings was a U.S. search and destroy operation conducted by the 3rd Brigade, 1
- Operation Black LionOperation Black Lion (15 June – 19 October 1972) was a Royal Lao Government counter-offens
- Operation Black Lion IIIOperation Black Lion III (18 October 1972 – 22 February 1973) was one of the last Royal La
- Operation Blue Star1984 Indian military operation
- Operation Booster ShotOperation Booster Shot was a rural aid program run by the United States in the Kingdom of
- Operation Burlington TrailOperation Burlington Trail was a security operation conducted during the Vietnam War by th
- Operation Bushmaster IIOperation Bushmaster II (also known as the Battle of Ap Nha Mat) was a US Army operation t
- Operation ByrdOperation Byrd was a security operation conducted during the Vietnam War by the U.S. 2nd B
- Operation Caban1979 French military operation in the Central African Republic
- Operation Car Wash2014-2021 Brazilian criminal investigation into corruption
- Operation Caroline HillOperation Caroline Hill was a security operation during the Vietnam War conducted by the 1
- Operation ChamberOperation Chamber was a military raid launched by the Rhodesian Security Forces (RSF) agai
- Operation Champaign GroveOperation Champaign Grove was a security operation during the Vietnam War conducted by ele
- Operation Coronado IIOperation Coronado II was the second of eleven in the Operation Coronado series conducted
- Operation Coronado IVOperation Coronado IV was the fourth of the Operation Coronado series of riverine military
- Operation Coronado IXOperation Coronado IX was a riverine military operation conducted by the Mobile Riverine F
- Operation Coronado XOperation Coronado X was the tenth of the Operation Coronado series of riverine military o
- Operation Coronado XIOperation Coronado XI was the eleventh of the Operation Coronado series of riverine milita
- Operation CounterpunchOperation Counterpunch, waged 26 September 1970 to 7 January 1971, was a military offensiv
- Operation Cyclone1970s–90s CIA program to fund Afghan militants
- Operation Deliberate Force1995 campaign by NATO and UN forces against Republika Srpska during the Bosnian War
- Operation Deny Flight1993–95 NATO operation in the Bosnian War
- Operation Desert RatOperation Desert Rat (16 February – 3 April 1971) was a diversionary attack by a Laotian i
- Operation Diamond ArrowOperation Diamond Arrow was a battle in southern Laos, waged from 20 September 1969 throug
- Operation DragnetOperation Dragnet was a security operation conducted by the 1st Cavalry Division in Bình Đ
- Operation Elk CanyonOperation Elk Canyon was a search and clear operation during the Vietnam War near Khâm Đức
- Operation Enterprise (Vietnam)Operation Enterprise was a U.S. Army pacification and security operation that took place i
- Operation Fa NgumOperation Fa Ngum (1–27 April 1972) was a Laotian military offensive aimed at capturing th
- Operation FarroupilhaOperation Farroupilha was the temporary transfer of the seat of government of the Brazilia
- Operation Fayette CanyonOperation Fayette Canyon was a security operation during the Vietnam War in Quảng Nam Prov
- Operation Francis MarionOperation Francis Marion was a 4th Infantry Division and 173rd Airborne Brigade operation
- Operation Frederick HillOperation Frederick Hill was a security operation during the Vietnam War in Quang Tin Prov
- Operation Frequent Wind1975 American operation of Vietnam War
- Operation Fulton SquareOperation Fulton Square was a joint U.S. Army and Army of the Republic of Vietnam (ARVN) m
- Operation GhaziOn 13 February 2017, Jamaat-ul-Ahrar released a video announcing the launch of "Operation
- Operation HardihoodOperation Hardihood was a security operation conducted from 16 May to 8 June 1966 during t
- Operation HardnoseOperation Hardnose was a Central Intelligence Agency-run espionage operation spying upon t
- Operation Harvest MoonOperation Harvest Moon/Lien Ket 18 was a US Marine Corps and Army of the Republic of Vietn
- Operation Haven DenialOperation Haven Denial was a U.S.-led operation (July 2–6, 2003) against Taliban remnants
- Operation Henderson HillOperation Henderson Hill was a US Marine Corps operation that took place in Happy Valley s
- Operation HickoryOperation Hickory was a search and destroy operation conducted by the 3rd Marine Division
- Operation HoustonOperation Houston was a security operation in the Vietnam War conducted by the United Stat
- Operation Idaho CanyonOperation Idaho Canyon was a United States Marine Corps operation in north-central Quảng T
- Operation Imperial LakeOperation Imperial Lake was a U.S. Marine Corps, Republic of Korea Marine Corps and U.S. A
- Operation Infinite Reach1998 American strikes in Afghanistan and Sudan
- Operation Iron MountainOperation Iron Mountain was a security operation during the Vietnam War in Quảng Ngãi Prov
- Operation JacanaOperation Jacana is the codename for a series of operations carried out by coalition force
- Operation Jackal1992 offensive of the Bosnian War
- Operation Junction City Jr.Operation Junction City Jr. was a major Laotian offensive of the Vietnam War; initially ai
- Operation KentuckyOperation Kentucky was a multi-battalion operation conducted by the United States Marine C
- Operation Lamar PlainOperation Lamar Plain was a security operation during the Vietnam War in Quảng Tín Provinc
- Operation LancasterOperation Lancaster was a U.S. Marine Corps operation that took place in northern Quảng Tr
- Operation Lancaster IIOperation Lancaster II was a U.S. Marine Corps security operation that took place in north
- Operation Left JabOperation Left Jab was the first military offensive launched against the Sihanouk Trail ex
- Operation Linda NchiKenyan military operation (2011–2012)
- Operation Maeng DaOperation Maeng Da was a Royal Lao Government military offensive aimed at disrupting the c
- Operation Maharat IIOperation Maharat II (31 December 1972 – 5 February 1973) was a Royalist offensive against
- Operation Maritime GuardOperation Maritime Guard was a NATO blockade, in the international waters of the Adriatic
- Operation Market TimeOperation Market Time was the United States Navy, Republic of Vietnam Navy and Royal Austr
- Operation MastiffOperation Mastiff was an operation conducted by the U.S. 1st Infantry Division in the Dầu
- Operation McLainOperation McLain (also known as Operation Dan Thang) was a security operation conducted du
- Operation Meade RiverOperation Meade River was a US Marine Corps cordon and search operation that took place so
- Operation Middlesex PeakOperation Middlesex Peak was a security operation during the Vietnam War conducted by the
- Operation MineralOperation Mineral was a military operation launched by the Rhodesian Security Forces again
- Operation Mistral 2Offensive by the Croatian Army and Croatian Defence Council
- Operation MongooseUS terrorism and sabotage campaign in Cuba
- Operation Mountain ResolveOperation Mountain Resolve was launched by a coalition led by the United States on 7 Novem
- Operation Mountain ViperIn Operation Mountain Viper, the United States Army and the Afghan National Army (nearly 1
- Operation MuscatineOperation Muscatine was a security operation conducted during the Vietnam War by the US Ar
- Operation Panther's ClawOperation Panchai Palang, or Panther's Claw, was a coalition military operation of the War
- Operation Pennsylvania SquareOperation Pennsylvania Square was a security operation during the Vietnam War conducted by
- Operation PershingOperation Pershing was an operation conducted by the 1st Cavalry Division, the 3rd Brigade
- Operation PhiboonpolOperation Phiboonpol (9–11 June 1971) was a "short but very intense engagement" of the Lao
- Operation Phou Phiang IIOperation Phou Phiang II (6 August – 25 October 1972) was one of the final battles of the
- Operation Phou Phiang IIIOperation Phou Phiang III (18 January – March 1973) was the final offensive of the Laotian
- Operation PhoutahOperation Phoutah (15 May – late September 1971) was one of a series of offensive operatio
- Operation Pickens ForestOperation Pickens Forest was a U.S. Marine Corps operation in Quảng Nam Province, South Vi
- Operation PigfatOperation Pigfat was a crucial guerrilla offensive of the Laotian Civil War; it lasted fro
- Operation PincushionOperation Pincushion was a covert training program for hill tribe recruits to become guerr
- Operation PiranhaOperation Piranha was a US Marine Corps operation during the Vietnam War that took place o
- Operation Pocahontas ForestOperation Pocahontas Forest was a security operation conducted during the Vietnam War by t
- Operation Pony ExpressOperation Pony Express was the covert transportation of, and the provision of aerial suppo
- Operation Prairie IIOperation Prairie II was a U.S. military operation in Quảng Trị Province, South Vietnam th
- Operation Prairie IIIOperation Prairie III was a U.S. Marine Corps operation in Quảng Trị Province, South Vietn
- Operation Prairie IVOperation Prairie IV was an operation conducted by the United States Marine Corps in the a
- Operation RaindanceOperation Raindance was a military operation of the Laotian Civil War, staged from 17 Marc
- Operation RedwingOperation Redwing was a United States series of 17 nuclear test detonations from May to Ju
- Operation Royal AmethystOperation Royal Amethyst was a military operation carried out by the Portuguese Guinean Ba
- Operation Rum PunchOperation Rum Punch or Operation Rampunch was a military action undertaken by United Natio
- Operation Sam HoustonOperation Sam Houston was a US Army operation that took place in the Plei Trap Valley and
- Operation SaratogaOperation Saratoga was a search and destroy operation during the Vietnam War conducted by
- Operation Scotland IIOperation Scotland II was a U.S. Marine Corps security operation that took place in northw
- Operation Searchlight1971 Pakistani army offensive
- Operation Shenandoah IIOperation Shenandoah II was a security operation conducted during the Vietnam War by the U
- Operation Silver BuckleOperation Silver Buckle (5 January – 11 February 1971), an offensive staged in Military Re
- Operation SinsayOperation Sinsay (11 February – c. 31 March 1972) was a Royal Lao Government offensive of
- Operation Sky MonitorOperation Sky Monitor was a NATO mission to monitor unauthorized flights in the airspace o
- Operation SmokescreenOperation Smokescreen was an American interagency counterterrorist operation to disrupt fu
- Operation SnoopyOperation Snoopy was an operation launched by Rhodesia in response to Air Rhodesia Flight
- Operation Speedy ExpressOperation Speedy Express was a controversial military operation conducted by the United St
- Operation Steel TigerOperation Steel Tiger was a covert U.S. 2nd Air Division, later Seventh Air Force and U.S.
- Operation Storm1995 military offensive and last major battle of the Croatian War of Independence
- Operation Storm-3331979 Soviet assassination of Afghan leader Hafizullah Amin
- Operation Strength IIOperation Strength II (6–31 March 1972) was a Royalist military offensive of the Laotian C
- Operation Summer '95Joint military offensive of the Croatian Army and the Croatian Defence Council
- Operation SwiftOperation Swift was a military operation in the Vietnam War, launched by units of the U.S.
- Operation Taylor CommonOperation Taylor Common was a search and destroy operation conducted by Task Force Yankee,
- Operation ThunderheadOperation Thunderhead was a highly classified combat mission conducted by U.S. Navy SEAL T
- Operation Tiger HoundOperation Tiger Hound was a covert U.S. 2nd Air Division, later Seventh Air Force and U.S.
- Operation Toan Thang IIOperation Toan Thang II ("Complete Victory") was an operation conducted by the US Army and
- Operation Toan Thang IVOperation Toan Thang IV ("Complete Victory") was a U.S. Army and Army of the Republic of V
- Operation Truong Cong DinhOperation Truong Cong Dinh (also known as Operation People's Road), was a United States an
- Operation UnaMilitary offensive by the Croatian Army against the Army of Republika Srpska
- Operation UnionOperation Union was a search and destroy mission in the Que Son Valley carried out by the
- Operation Union IIOperation Union II was a search and destroy mission in the Quế Sơn Valley carried out by t
- Operation United ShieldOperation United Shield was the codename of a military operation, conducted 9 January to 3
- Operation Uphold DemocracyInternational military intervention in Haiti following the 1991 coup d'etat
- Operation Warrior SweepOperation Warrior Sweep was a 2003 operation in the War in Afghanistan. It involved a July
- Operation Winter '941994 battle of the Croatian War of Independence and the Bosnian War
- Operation WishboneOperation Wishbone was a military operation in Angola during December 1980 by the South Af
- Oppose Book Worship1930 essay by Mao Zedong
- Opposition to United States involvement in the Vietnam War1965–1973 anti-war movement
- Orange Revolution2004–2005 political protests in Ukraine
- Orientalium EcclesiarumDecree on the Eastern Catholic Churches
- Origins of Hutu, Tutsi and TwaThe origins of the Hutu, Tutsi and Twa peoples is a major issue of controversy in the hist
- Oshika PeninsulaThe Oshika Peninsula (牡鹿半島, Oshika-hantō) also pronounced "Ojika" is a peninsula which pro
- Oslo Accords1990s Israeli–Palestinian peace agreements
- Ottoman campaign against HormuzThe Ottoman campaign against Hormuz took place in 1552–1554. An Ottoman fleet led by Admir
- Our Poisoned LandOur Poisoned Land: Living in the Shadows of Zuma's Keepers a 2022 book by Jacques Pauw, a
- Outright Monetary TransactionsOutright Monetary Transactions (OMT) is a program of the European Central Bank under which
- Oval OfficeUS presidential office in the White House
- Overseas landholdings of the Marcos familyHoldings of Ferdinand and Imelda Marcos
- Overthrow of Slobodan Milošević2000 overthrow of Yugoslav President Slobodan Milošević