1,303 articles
Pereiaslav Agreement
Pereiaslav Agreement (Pereiaslav Council, Переяславська рада): the 1654 Ukrainian-Muscovite settlement in which Hetman Bohdan Khmelnytsky's Cossack Hetmanate placed itself under Tsar Alexei Mikhailovich's protection, completed by the March Articles; contested as alliance, protectorate, or 'reunification.'
Peremptory norm
Peremptory norm (jus cogens) in international law: a norm from which no derogation is permitted, hierarchically superior, voiding conflicting treaties, codified in VCLT Article 53 and codified in ILC 2022 draft conclusions.
Perfidy
Perfidy is the war crime of feigning a protected status under international humanitarian law, such as surrender, civilian status, or the red cross emblem, to kill, injure, or capture an adversary; distinct from lawful ruses of war like camouflage and ambush.
Permanent Court of Arbitration
Permanent Court of Arbitration (PCA), Hague-based intergovernmental arbitration body created by the 1899 Hague Convention, operating since 1902; panel-based, consensual institution with 129 contracting parties administering 251 cases in 2025.
Permanent Court of International Justice
Permanent Court of International Justice (Cour permanente de Justice internationale), the League of Nations' World Court at the Peace Palace, The Hague; sat 1922 to 1946, heard 29 contentious cases and 27 advisory opinions, and was succeeded by the ICJ.
Permanent Mandates Commission
Permanent Mandates Commission (Commission permanente des mandats), League of Nations advisory body under Article 22 of the Covenant, supervised fifteen mandated territories from Geneva, 1921 to 1946, before the UN Trusteeship Council replaced it.
Permanent Mandates Commission (Palestine)
The Permanent Mandates Commission (PMC) was the League of Nations expert body, sitting in Geneva from October 1921 to 1939, that examined mandatory powers' annual reports and petitions and advised the Council, including on the British Mandate for Palestine through the 1929 disturbances, the 1937 partition debate, and the 1939 White Paper.
Perry Expedition
Perry Expedition: 1853-1854 US naval mission under Commodore Matthew C. Perry whose Black Ships gunboat diplomacy produced the Treaty of Kanagawa, opening Shimoda and Hakodate and ending Tokugawa Japan's trade seclusion.
Persistent objector rule
The persistent objector rule, or persistent objector doctrine, lets a State avoid a customary international law norm by clearly objecting during its formation and maintaining that objection; codified in ILC Draft Conclusion 15 (2018), inapplicable to jus cogens.
Persona non grata
Persona non grata (Latin, "unwelcome person") is the diplomatic status under Article 9 of the 1961 Vienna Convention by which a host state expels a diplomat, usually for espionage, without giving reasons, typically triggering reciprocal expulsions.
Pheasant Island
Pheasant Island (Île des Faisans, Isla de los Faisanes) is an uninhabited islet in the Bidasoa river between France and Spain, the world's smallest condominium, changing sovereignty every six months and site of the 1659 Treaty of the Pyrenees.
Philip Morris v. Uruguay
Philip Morris v. Uruguay (ICSID ARB/10/7) was an investor-state arbitration under the 1988 Switzerland-Uruguay BIT challenging Uruguay's 80% health warnings and single presentation rule; all claims were dismissed on 8 July 2016.
Philippines v. China
Philippines v. China, PCA Case 2013-19, an Annex VII UNCLOS arbitration filed 22 January 2013; China refused participation; the 12 July 2016 award invalidated the nine-dash line historic-rights claim.
Pierre Lalive d'Epinay
Pierre Lalive d'Epinay (1923–2014) was a Swiss law professor at the University of Geneva, called the grand old man of Swiss arbitration and the 1990 Balzan Prize laureate for private international law.
Pierre Pigneau de Behaine
Pierre Pigneau de Behaine (Bá Đa Lộc, 1741–1799), French MEP missionary, titular bishop of Adran, and vicar apostolic of Cochinchina, negotiated the 1787 Treaty of Versailles between Louis XVI and Nguyễn Ánh and aided his return to power.
Pinochet case (R v Bow Street Metropolitan Stipendiary Magistrate, ex parte Pinochet)
The Pinochet case was a 1998–1999 English extradition proceeding in which former Chilean head of state Augusto Pinochet, arrested in London, was denied immunity for torture.
Piracy
Piracy: illegal acts of violence or depredation for private ends on the high seas under UNCLOS article 101, distinct from armed robbery against ships in territorial waters; tracked by IMO and ICC IMB, with 137 incidents in 2025 and Somali resurgence.
Platt Amendment
Platt Amendment: 1901 US rider to the Army Appropriations Bill, drafted by Elihu Root and named for Senator Orville Platt, defining US-Cuba relations; treaty of May 22, 1903; gave the US intervention rights and the Guantánamo Bay lease; repealed 1934.
Poitou
Poitou, historic province of western France around Poitiers (Pictones/Pictavi), divided into Upper and Lower Poitou; county of the Ramnulfid counts-dukes, Plantagenet from 1152, French from 1204/1259, annexed 1369–1373.
Population exchange between Greece and Turkey
The population exchange between Greece and Turkey, agreed at Lausanne in 1923, forcibly transferred about 1.2 million Greek Orthodox Christians and 500,000 Muslims between the two countries.
Pragmatic Sanction of 1713
Pragmatic Sanction of 1713 (Pragmatische Sanktion), succession law of Emperor Charles VI issued 19 April 1713 declaring Habsburg lands indivisible with female succession; basis of the monarchy until 1918 and trigger of the War of the Austrian Succession.
Preemptive war
Preemptive war is first use of force against an imminent attack, distinguished from preventive war against a distant potential threat. Defined by the Caroline criteria, constrained by UN Charter Articles 2(4) and 51, tested in 1967, 1981, and Iraq 2003.
Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization
The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization is an international body in Vienna, Austria, that operates the International Monitoring System and detected North Korea's nuclear tests.
Prescriptive jurisdiction
Prescriptive jurisdiction is a state's authority to make its law applicable to persons, conduct, relations, or interests, one part of the tripartite division alongside enforcement and adjudicative jurisdiction.
Presidential statements of the United Nations Security Council
A presidential statement of the United Nations Security Council is a statement by the Council's President on behalf of all members, adopted by consensus rather than vote.
Prevention of an Arms Race in Outer Space
Prevention of an Arms Race in Outer Space, known as PAROS, is a United Nations diplomatic initiative seeking a treaty against weapons in orbit, on the agenda since 1982.
Prevlaka
Prevlaka is a small uninhabited peninsula at the southern tip of Croatia, at the entrance to the Bay of Kotor on the border with Montenegro.
Prevlaka dispute
Prevlaka dispute: Croatia–Montenegro border disagreement over Cape Oštro at the Bay of Kotor entrance, monitored by UNMOP 1996–2002, governed since by the unratified 2002 interim protocol.
Principality of Elba
Principality of Elba (Principato d'Elba): short-lived sovereign state created for Napoleon by the Treaty of Fontainebleau, 11 April 1814; he ruled the island's 12,000 inhabitants from Portoferraio for less than ten months before escaping on 26 February 1815.
Procedure before international arbitral tribunals
Procedure before international arbitral tribunals is the set of rules governing how an arbitration between sovereign States is conducted, from tribunal constitution to the award.