A reversion in property law is a future interest that is retained by the grantor after the conveyance of an estate of a lesser quantum than he has (such as the owner of a fee simple granting a life estate or a leasehold estate). Once the lesser estate comes to an end (the lease expires or the life estate tenant dies), the property automatically reverts (hence reversion) back to the grantor.
Territorial reversion
Unlike private-law reversion, territorial reversion concerns sovereign rights over states or principalities and was common in early modern and nineteenth-century Europe
[A notable example of territorial reversion occurred after the death of Marie Louise of Austria in 1847. Under the arrangements established by the Congress of Vienna (1815), the Duchy of Parma, which she held for life, reverted to the Bourbon-Parma dynasty, while the Duchy of Lucca, governed by the same dynasty, was in turn to revert to the Grand Duchy of Tuscany. An earlier example can be found in the history of the House of Este. While the Este retained the Duchy of Modena and Reggio as an imperial fief, the Duchy of Ferrara, held as a papal fief, reverted to the Papal States in 1598 following the extinction of the legitimate Este line recognized by the Holy See.]. It was is a principle of
Public law and dynastic law by which a territory returns to a previous sovereign or ruling house upon the extinction of a ruling line or the occurrence of a condition provided for in treaties, dynastic statutes, or acts of investiture.
