Impossibility of Execution.
§ 542. All treaties whose execution becomes impossible subsequent to their conclusion are thus rendered void. A frequently quoted example is that of three States concluding a treaty of alliance and subsequent war breaking out between two of the contracting parties. In such case it is impossible for the third party to execute the treaty, and it becomes void.[907] It must, however, be added that the impossibility of execution may be temporary only, and that then the treaty is not void but merely suspended.
[907] See also above, § [521], where the case is mentioned that a treaty essentially presupposes a certain form of government, and for this reason cannot be executed when this form of government undergoes a change.
Realisation of Purpose of Treaty other than by Fulfilment.
§ 543. All treaties whose purpose is realised otherwise than by fulfilment become void. For example, a treaty concluded by two States for the purpose of inducing a third State to undertake a certain obligation becomes void if the third State voluntarily undertakes the same obligation before the two contracting States have had an opportunity of approaching the third State with regard to the matter.
Extinction of such Object as was concerned in a Treaty.
§ 544. All treaties whose obligations concern a certain object become void through the extinction of such object. Treaties, for example, concluded in regard to a certain island become void when such island disappears through the operation of nature, as likewise do treaties concerning a third State when such State merges in another.
XI CANCELLATION OF TREATIES
See the literature quoted at the commencement of § [534].