novation

Novation, in contract law and business law, is the act of – replacing an obligation to perform with another obligation; or adding an obligation to perform; or replacing a party to an agreement with a new party.

In international law, novation is the acquisition of territory by a sovereign state through "the gradual transformation of a right in territorio alieno [in foreign territory] into full sovereignty without any formal and unequivocal instrument to that effect intervening".