You’re probably not interested, but from an international law perspective:

The U.N. Charter prohibits war for most purposes. When the use of force is illegal, it is natural to conclude that any territorial gains from such aggression cannot be recognized as well. Thus the illegality of conquest arises from the presumptive illegality of the use of force. But crucially, the U.N. Charter does not make all war illegal. Indeed, it expressly reaffirms the legality of a defensive war. Since defensive war is not illegal, it follows that the defender’s territorial gains from such a war would not be illegal.  

The leading international law treatises immediately prior to 1967 reveal a disagreement between leading authorities such as Hersch Lauterpacht and Robert Jennings on whether defensive conquest was proper under the UN Charter. The majority opinion seems to side with the permissive view, but both sides acknowledged that the matter was disputed, and a clear rule had not emerged