Threat of force in public international law is a situation between states described by British

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 lawyer Ian Brownlie

Ian Brownlie

Sir Ian Brownlie, CBE, QC, FBA was a British practising barrister, specialising in international law. After an education at Hertford College, Oxford, he was called to the Bar by Gray's Inn in 1958 and was a tenant at Blackstone Chambers from 1983 until his death on 3 January 2010.During his...

 as:

an express or implied promise by a government of a resort to force conditional on non-acceptance of certain demands of that government.

The 1969 Vienna convention on the Law of Treaties notes in its preamble that both the threat and the use of force are prohibited. Moreover, in Article 52, it establishes the principle that if threats of using force are made during diplomatic negotiations, then any resulting treaty is invalid, stating "A treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations".

Further reading

• Stürchler, Nikolas. (August 13, 2007). The Threat of Force in International Law. Series: Cambridge Studies in International and Comparative Law (No. 53). Cambridge University Press
  Cambridge University Press
  Cambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by Henry VIII in 1534, it is the world's oldest publishing house, and the second largest university press in the world...
  
  . ISBN 0-521-87388-6.
• World Court Digest web page referring to threat of force.