It is possible to adopt the child internationally under the adoption law of USA. You must have to abide the adoption law and also see the law of the country where you need to adopt the child. Suppose you are adopting the child from UK than you must have to see the UK based child adoption agency and get the details about the adoption of child. You also need to abide the rules of the each country too.
If you are adopting the child in blood relation than you have separate law. You also need to get the details about the adoption of child in blood relation.
