Within the Holy Roman Empire different titles were used by nobles exercising various degrees of sovereignty within their borders (see below). Such titles were granted or recognised by the Emperor or Pope. Adoption of a new title to indicate sovereign or semi-sovereign status was not always recognized by other governments or nations, sometimes causing diplomatic problems.
During the nineteenth century many small monarchies in Europe merged with other territories to form larger entities, and following World War I and World War II, many monarchies were abolished, but of those remaining all except Luxembourg, Liechtenstein, Andorra, Vatican City and Monaco were headed by a king or queen.