Misunderstanding, fraud, corruption, coercion
Articles 46-53 of the Vienna Convention 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 the circumstances by which a state party joined the treaty, 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.
A state's consent may be invalidated if there was an erroneous understanding of a fact or situation at the time of conclusion, which formed the "essential basis" of the state's consent. Consent will not be invalidated if the misunderstanding was due to the state's own conduct, or if the truth should have been evident.
Consent will also be invalidated if it was induced by the fraudulent conduct of another party, or by the direct or indirect "corruption" of its representative by another party to the treaty. Coercion of either a representative, or the state itself through the threat or use of force, if used to obtain the consent of that state to a treaty, will invalidate that consent.
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Adoption for the Well-Born
Adoption has been called the quintessential American institution, embodying faith in social engineering and mobility.  While it is true that the modern form of adoption emerged in the United States, Western civilization has a long history of the practice of adoption. The Code of Hammurabi, for example, details the rights of adopters and the responsibilities of adopted individuals at length while the practice of adoption in ancient Rome is well documented in the Codex Justinianus.  
Ancient adoption practices were markedly different from those in the modern period. Foremost, they were legal tools that strengthened political ties between wealthy families and provided male heirs to manage the estates of other notables.   Adoption was inherently an act that fostered the interests of adults, putting less emphasis on the interests of those adopted.  The use of adoption along these lines by the aristocracy is well documented; many of the emperors of Rome were adopted sons.
Moreover, evidence suggests that although legal, infant adoption for the purpose of building a family was rare.   The abandoned were often picked up for slavery rather than adoption.  In fact, abandoned children are thought to have composed a significant percentage of the Empire’s slave supply.  Evidence of trafficking abandoned children also comes from the Church Fathers. Both Clement of Alexandria and Justin Martyr attest that foundlings of both genders made up a substantial portion of those in brothels. 
Nevertheless, Roman legal records indicate that some foundlings were taken in by families and raised as one of their own. Such children, however, were not normally adopted. Called alumni, they were more similar to modern foster children and still considered the property of the father who abandoned them. 
Other ancient civilizations, notably India and China, utilized some form of adoption as well. Evidence suggests their practices aimed to ensure the continuity of cultural and religious practices rather than the creation of new families. In ancient India, for example, ‘secondary sonship’ was clearly denounced by the Rigveda,  yet the practice continued, in a limited and highly ritualistic form, so that an adopter might have the necessary funerary rights performed by a son.  China had a similar conception of adoption; males were adopted in order to carry on the duty of ancestor worship.  Western ideas of adoption would not take hold in the East until well into the contemporary period.
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(*Adoption is a whiteman's word*)