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Casus belli

Casus belli

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is a Latin expression meaning the justification for acts of war. means "incident", "rupture" or indeed "case", while means bellic ("of war"). It is usually distinguished from , with being used to refer to offenses or threats directly against a nation, and to refer to offenses or threats to another, allied, nation with which the justifying nation is engaged in a mutual defense treaty, such as NATO.

Hugo Grotius
Hugo Grotius , also known as Huig de Groot, Hugo Grocio or Hugo de Groot, was a jurist in the Dutch Republic. With Francisco de Vitoria and Alberico Gentili he laid the foundations for international law, based on natural law...

 (1653), Cornelius van Bynkershoek (1707), and Jean-Jacques Burlamaqui
Jean-Jacques Burlamaqui
Jean-Jacques Burlamaqui was a Swiss legal and political theorist, who popularised a number of ideas propounded by other thinkers.-Life:...

 (1732), among others, and the rise of the political doctrine

 of jus ad bellum
Jus ad bellum
Jus ad bellum is a set of criteria that are to be consulted before engaging in war, in order to determine whether entering into war is permissible; that is, whether it is a just war....

or "just war
Just War
Just war theory is a doctrine of military ethics of Roman philosophical and Catholic origin, studied by moral theologians, ethicists and international policy makers, which holds that a conflict ought to meet philosophical, religious or political criteria.-Origins:The concept of justification for...


Formally, a government would lay out its reasons for going to war, as well as its intentions in prosecuting it and the steps that might be taken to avert it. In so doing, the government would attempt to demonstrate that it was going to war only as a last resort (ultima Ratio) and that it in fact possessed "just cause" for doing so. In theory international law
International law

 today allows only three situations as legal cause to go to war: out of self-defense, defense of an ally under a mutual defense pact, or sanctioned by the UN.

Proschema (plural proschemata) is the Greek equivalent term. The stated reasons may or may not be the actual reason for waging the war (prophasis
In Greek mythology, Prophasis was the personification of excuse or plea. She was called the daughter of Epimetheus....

). The term was first popularized by Thucydides
Thucydides was a Greek historian and author from Alimos. His History of the Peloponnesian War recounts the 5th century BC war between Sparta and Athens to the year 411 BC...

 in his History of the Peloponnesian War, who identified fear, honor, and interest as the three primary real reasons that wars are waged, while proschemata commonly play up nationalism or fearmongering (as opposed to rational or reasonable fears).

Reasons for use


War of aggression

. In effect, this means that countries in the modern era must have a plausible for initiating military action, or risk UN sanctions or intervention.

Historical examples

This section outlines a number of the more famous or controversial cases of casus belli which have occurred in modern times.

Spanish-American War

The casus belli for the Spanish-American War
Spanish-American War

 was the sinking of the USS Maine
USS Maine (ACR-1)
USS Maine was the United States Navy's second commissioned pre-dreadnought battleship, although she was originally classified as an armored cruiser. She is best known for her catastrophic loss in Havana harbor. Maine had been sent to Havana, Cuba to protect U.S. interests during the Cuban revolt...


There have been several alternative explanations to the explosion such as that proposed by Mr. Evans, the senior editor of Newsweek. In his book, he states that the USS Maine was designed incorrectly because the boiler room was right next to the gunpowder storage room and that an overheating in the boiler room may have heated the adjacent metal wall that caused the powder to explode.

World War I

A political assassination provided the trigger that led to the outbreak of World War I
World War I

. In June 1914, the refusal of two points in the July Ultimatum
July Ultimatum
The July Crisis was a diplomatic crisis among the major powers of Europe in the summer of 1914 that led to the First World War...

 offered to Serbia, was used by Austria-Hungary

 as a casus belli for declaring war on Serbia

. The Assassination of Archduke Franz Ferdinand of Austria
Assassination of Archduke Franz Ferdinand of Austria

 at Sarajevo
Sarajevo |Bosnia]], surrounded by the Dinaric Alps and situated along the Miljacka River in the heart of Southeastern Europe and the Balkans....

 in Austria-Hungary

 by Gavrilo Princip
Gavrilo Princip
Gavrilo Princip was the Bosnian Serb who assassinated Archduke Franz Ferdinand of Austria and his wife, Sophie, Duchess of Hohenberg, in Sarajevo on 28 June 1914...

, a Serbian

 nationalist from Bosnia, Austrian subject and member of Young Bosnia
Young Bosnia
Young Bosnia was a revolutionary movement active before World War I, the members were predominantly school students who were ethnic Serbs, but included Bosniaks...

, was the reason why this ultimatum was made.

The Russian Empire
Russian Empire

 started to mobilise its troops in defence of its ally Serbia, which resulted in the German Empire
German Empire

 declaring war on Russia in support of its ally Austria-Hungary. Very quickly, after the involvement of France

, the Ottoman Empire
Ottoman Empire

 and the British Empire
British Empire

, five of the six great European powers became involved in the first European general war since the Napoleonic Wars
Napoleonic Wars


World War II

In his autobiography Mein Kampf
Mein Kampf

, Adolf Hitler
Adolf Hitler

 had in the 1920s advocated a policy of lebensraum

("living space") for the German people

, which in practical terms meant German territorial expansion into Eastern Europe.

In August 1939, in order to implement the first phase of this policy, Germany

's Nazi government under Hitler's leadership staged the Gleiwitz incident
Gleiwitz incident
The Gleiwitz incident was a staged attack by Nazi forces posing as Poles on 31 August 1939, against the German radio station Sender Gleiwitz in Gleiwitz, Upper Silesia, Germany on the eve of World War II in Europe....

, which was used as a for the invasion of Poland the following September. Poland

's allies Britain
United Kingdom

 and France

 honoured their alliance and subsequently declared war on Germany.

In 1941, acting once again in accordance with the policy of lebensraum, Nazi Germany
Nazi Germany

 invaded the Soviet Union
Operation Barbarossa

, using the casus belli of pre-emptive war to justify the act of aggression.

The Soviet Union
Soviet Union

 also employed a manufactured casus belli against Finland

 during World War II on its part. In November 1939, shortly after the outbreak of hostilities between Germany, Britain and France, the Soviet Union staged the shelling
Shelling of Mainila
The Shelling of Mainila was a military incident on November 26, 1939, where the Soviet Union's Red Army shelled the Russian village of Mainila , declared that the fire originated from Finland across a nearby border and claimed losses in personnel...

 of the Russian village of Mainila, which it blamed on the Finns. This manufactured incident was then used as a casus belli for the Winter War
Winter War

. In 1998, Russian President Boris Yeltsin
Boris Yeltsin
Boris Nikolayevich Yeltsin was the first President of the Russian Federation, serving from 1991 to 1999.Originally a supporter of Mikhail Gorbachev, Yeltsin emerged under the perestroika reforms as one of Gorbachev's most powerful political opponents. On 29 May 1990 he was elected the chairman of...

 admitted that the invasion had in fact constituted a Soviet war of aggression
War of aggression


Six-Day War

A casus belli played a prominent role during the Six-Day War
Six-Day War
The Six-Day War , also known as the June War, 1967 Arab-Israeli War, or Third Arab-Israeli War, was fought between June 5 and 10, 1967, by Israel and the neighboring states of Egypt , Jordan, and Syria...

 of 1967. The Israeli government had a short list of , acts that it would consider provocations justifying armed retaliation. The most important was a blockade of the Straits of Tiran
Straits of Tiran
The Straits of Tiran , are the narrow sea passages, about wide, between the Sinai and Arabian peninsulas which separate the Gulf of Aqaba from the Red Sea...

 leading into Eilat, Israel's only port to the Red Sea
Red Sea

, through which Israel received much of its oil. After several border incidents between Israel and Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

's allies Syria

 and Jordan
Jordan , officially the Hashemite Kingdom of Jordan , Al-Mamlaka al-Urduniyya al-Hashemiyya) is a kingdom on the East Bank of the River Jordan. The country borders Saudi Arabia to the east and south-east, Iraq to the north-east, Syria to the north and the West Bank and Israel to the west, sharing...

, Egypt expelled UNEF
United Nations Emergency Force
The first United Nations Emergency Force was established by United Nations General Assembly to secure an end to the 1956 Suez Crisis with resolution 1001 on November 7, 1956. The force was developed in large measure as a result of efforts by UN Secretary-General Dag Hammarskjöld and a proposal...

 peacekeepers from the Sinai Peninsula
Sinai Peninsula
The Sinai Peninsula or Sinai is a triangular peninsula in Egypt about in area. It is situated between the Mediterranean Sea to the north, and the Red Sea to the south, and is the only part of Egyptian territory located in Asia as opposed to Africa, effectively serving as a land bridge between two...

, established a military presence at Sharm el-Sheikh
Sharm el-Sheikh

, and announced a blockade of the straits, prompting Israel to cite its casus belli in opening hostilities against Egypt.

Vietnam War

Many historians have suggested that the Gulf of Tonkin Incident
Gulf of Tonkin Incident
The Gulf of Tonkin Incident, or the USS Maddox Incident, are the names given to two incidents, one fabricated, involving North Vietnam and the United States in the waters of the Gulf of Tonkin...

 was a manufactured pretext for the Vietnam War
Vietnam War

. North Vietnamese Naval officials have publicly stated that the USS Maddox
USS Maddox (DD-731)
USS Maddox , an was named for Captain William A. T. Maddox, USMC. She was laid down by the Bath Iron Works Corporation at Bath in Maine on 28 October 1943, launched on 19 March 1944 by Mrs. Harry H...

 was never fired on by North Vietnamese naval forces.In the movie "The Fog of War", then US Defense Secretary Robert McNamara
Robert McNamara

 concedes the attack did not happen, though he says that he and President Johnson believed it did so at the time.

Some people confuse the first Gulf of Tonkin Incident (the 2nd of August) and the second Gulf of Tonkin Incident (the 4th of August). The North Vietnamese claimed that on August 2 US destroyer USS Maddox was hit by one torpedo, and one of the American aircraft had been shot down in North Vietnamese territorial waters. The PAVN Museum in Hanoi displays "Part of a torpedo boat... which successfully chased away the USS Maddox August, [sic] 2nd 1964".

The casus belli for the Vietnam War was the second incident. On August 4 USS Maddox was launched to the North Vietnamese coast in order to "show the flag" after the first incident. The U.S. authorities claimed that two Vietnamese boats tried to attack USS Maddox and were sunk. The government of North Vietnam denied the second incident completely. Deniability played favorably into the propaganda efforts of North Vietnam throughout the war, and for some years to follow.

1982 Israeli Invasion of Lebanon

The cited by Israel for its June 1982 invasion of Lebanon
1982 Lebanon War
The 1982 Lebanon War , , called Operation Peace for Galilee by Israel, and later known in Israel as the Lebanon War and First Lebanon War, began on 6 June 1982, when the Israel Defense Forces invaded southern Lebanon...

 was the attempted assassination of the Israeli Ambassador in London, which the Israeli government blamed on the Palestinian Liberation Organization. A possible invasion plan had been prepared in advance by Israel.

Greece and Turkey

In 1995, The Turkish Parliament
Grand National Assembly of Turkey
The Grand National Assembly of Turkey , usually referred to simply as the Meclis , is the unicameral Turkish legislature. It is the sole body given the legislative prerogatives by the Turkish Constitution. It was founded in Ankara on 23 April 1920 in the midst of the Turkish War of Independence...

 issued a against Greece

 in reaction to an enacted extension of Greek territorial waters
Territorial waters
Territorial waters, or a territorial sea, as defined by the 1982 United Nations Convention on the Law of the Sea, is a belt of coastal waters extending at most from the baseline of a coastal state...

 from 6 nautical miles (11 km) to 12 nautical miles (22 km) from the coast.

War on Terror

The for the Bush administration
George W. Bush administration
The presidency of George W. Bush began on January 20, 2001, when he was inaugurated as the 43rd President of the United States of America. The oldest son of former president George H. W. Bush, George W...

's conceptual War on Terror
War on Terror
The War on Terror is a term commonly applied to an international military campaign led by the United States and the United Kingdom with the support of other North Atlantic Treaty Organisation as well as non-NATO countries...

, which resulted in the 2001 Afghanistan war
War in Afghanistan (2001–present)

 and the 2003 Iraq war, was the September 11, 2001 attacks
September 11, 2001 attacks

 on the World Trade Center
World Trade Center

 in New York City
New York City

, The Pentagon
The Pentagon

 in Arlington, Virginia and the apparently intended attack on the United States Capitol
United States Capitol

 in Washington, D.C.
Washington, D.C.

2003 Invasion of Iraq

When the United States invaded Iraq in 2003
2003 invasion of Iraq

, it cited Iraq's non-compliance with the terms of cease-fire agreement for the 1990-1991 Gulf War
Gulf War
The Persian Gulf War , commonly referred to as simply the Gulf War, was a war waged by a U.N.-authorized coalition force from 34 nations led by the United States, against Iraq in response to Iraq's invasion and annexation of Kuwait.The war is also known under other names, such as the First Gulf...

, as well as planning in 1993 attempted assassination of former President George Bush Sr. and firing on coalition aircraft enforcing the no-fly zones
Iraqi no-fly zones
The Iraqi no-fly zones were a set of two separate no-fly zones , and were proclaimed by the United States, United Kingdom and France after the Gulf War of 1991 to protect the Kurdish people in northern Iraq and Shiite Muslims in the south. Iraqi aircraft were forbidden from flying inside the zones...

 as its stated .

Cited by the Bush administration was Saddam Hussein
Saddam Hussein

's weapons of mass destruction
Weapons of mass destruction
A weapon of mass destruction is a weapon that can kill and bring significant harm to a large number of humans and/or cause great damage to man-made structures , natural structures , or the biosphere in general...

 (WMD) program. The administration claimed that Iraq had not conformed with its obligation to disarm under past UN Resolutions, and that Saddam Hussein was actively attempting to acquire a nuclear weapons capability as well as enhance an existing arsenal of chemical and biological weapons. Secretary of State Colin Powell
Colin Powell

 addressed a plenary session of the United Nations Security Council
United Nations Security Council

on February 5, 2003 citing these reasons as justification for military action.