Articles 46–53 of the Vienna Convention on the Law of Treaties set out the only ways that treaties can be invalidated—considered unenforceable and void under international law. A treaty will be invalidated due to either <answer>the circumstances by which a state party joined the treaty</answer>, or due to the content of the treaty itself. Invalidation is separate from withdrawal, suspension, or termination (addressed above), which all involve an alteration in the consent of the parties of a previously valid treaty rather than the invalidation of that consent in the first place.
In addition to the content of the treaty itself, why might a treated by invalidated?
the circumstances by which a state party joined the treaty