A more thorough explanation:

Definition: Clausa rebus sic stantibus is a Latin term used in international law. It refers to a treaty provision that states that the treaty is binding only as long as the circumstances in existence when the treaty was signed remain substantially the same. If there is a fundamental change in circumstances that alters the essential basis for the parties' consent to be bound by the treaty and radically transforms the extent of the parties' performances under the treaty, then the doctrine of clausa rebus sic stantibus may be invoked. However, this doctrine does not apply to treaties establishing boundaries.

Example: Suppose two countries sign a treaty to share water resources from a river. If a drought occurs and the river dries up, then the treaty may no longer be valid because the essential basis for the parties' consent to be bound by the treaty has been altered. In this case, the doctrine of clausa rebus sic stantibus may be invoked to release the parties from their obligations under the treaty.

Explanation: This example illustrates how the doctrine of clausa rebus sic stantibus may be applied when there is a fundamental change in circumstances that alters the essential basis for the parties' consent to be bound by the treaty. In this case, the drought has radically transformed the extent of the parties' performances under the treaty, making it impossible for them to fulfill their obligations. Therefore, the doctrine of clausa rebus sic stantibus may be invoked to release the parties from their obligations under the treaty.