Caroline criteria

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The Caroline criteria (after the American steamer Caroline) are the criteria recognized under international law for the exercise of the right of self-defense by states. Their formulation is also known as the Webster formula - named after the American Secretary of State Daniel Webster .

These criteria are an immediate, overriding necessity for self-defense that leaves no choice of means and no time for further consideration (“ a necessity of self-defense, instant, overwhelming, leaving no choice of means, and no moment for deliberation ”). The measures taken must not be absurd or excessive (“ nothing unreasonable or excessive ”).


The Caroline criteria were fixed in 1842 in a diplomatic exchange of notes and letters between the USA and Great Britain . Before that, the Caroline / McLeod affair had occurred. In December 1837, British forces had forcibly taken possession of and destroyed the US steamer Caroline on the US side of the Niagara River . The British government was fighting riots in Canada at the time . The insurgents used US territory as a retreat and called for support with weapons and volunteers. The USA, on the other hand, had basically taken measures to maintain its neutrality , but in some cases encountered difficulties in enforcing them because of the sympathy for the insurgents among its own population. It was later undisputed that around 1,000 armed men - mainly US Americans - had been assembled with the Caroline on an island that was already British territory.

The British government declared the nightly storming of the ship, which was still occupied with passengers, which resulted in two deaths, and its setting on fire, after which it drifted over Niagara Falls , as legitimate self-defense. The USA recognized the right to self-defense in principle. However, in the specific case they denied their existence and asserted the criteria mentioned, which were recognized by Great Britain as relevant.

As a result, the Caroline criteria were repeatedly used as a yardstick by all sides in conflicts, which made them customary under international law .


  • Claus Kreß & Björn Schiffbauer: First sunk, then elevated to international law. How a steamship called Caroline still moves international law today. In: Legal worksheets . No. 8/9, 2009, p. 611 ( PDF )
  • 1842 exchange of letters between the US Secretary of State and Her Majesty Plenipotentiary Minister on Special Mission Lord Ashburton, commented by David Hunter Miller. In: David Hunter Miller (Ed.): Treaties and Other International Acts of the United States of America. Vol. 4: Documents 80-121: 1836-1846. United States Government Printing Office , Washington 1934

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