Mediatization, defined broadly, is the subsumation of one monarchy into another monarchy in such a way that the ruler of the annexed state keeps his or her sovereign title and, sometimes, a measure of local power. For instance: when a sovereign county is annexed to a larger principality, its reigning count might find himself subordinated to a prince, but nevertheless remains a count, and one of sovereign rank, if not actually fully sovereign in deed. His subjects exercise their allegiance to the higher prince through him, and so his sovereignity is said to be mediatised, as in, "through the medium of".
The term "mediatization" was originally applied to the reorganization of the German states during the early 19th century, although the process had been going on since the Middle Ages. Mediatization has occurred in a number of other countries: Italy (e.g., Orsini, Doria, Pallavicini), Russia (e.g., Sibirsky, Vorotynsky), and France (e.g.,Rohan, de Bouillon and Lorraine) are notable examples.
Mediatized sovereign houses rank higher than other houses of nominally equal (or higher) rank, but who never ruled a state. This division had great social significance, as mediatized princes were considered equal to royals for marriage purposes; in essence they were regarded as royalty. Thus if a scion from the most obscure mediatized family (say the child of an impoverished mediatized count) married an emperor or a king, their alliance was considered equal, not morganatic, and their children could inherit dynastic rights. Thus the children of Ernst Count zu Lippe-Biesterfeld, though the children of a Count, were called princes, and the son of his second son, Prince Bernhard of Lippe-Biesterfeld, was fit to marry Juliana, Crown Princess, later Queen, of the Netherlands and their eldest daughter, Beatrix, today occupies the Dutch throne. This is one of the reasons why so many monarchs married German princes: German mediatized families were especially abundant.
The authoritative guide to the royal and noble houses of Europe, the Almanach de Gotha, is divided into three sections: sovereign houses, mediatized houses, and other noble houses.
The legal basis for mediatization was the Reichsdeputationshauptschluss of 1803, which had become necessary under pressure from France. The Treaty of the Confederation of the Rhine of 1806 continued the process of mediatization. The constitution of the German Confederation of 1815 confirmed the mediatization, but gave certain rights to the mediatized princes, such as first instance jurisdiction.
Morganatic marriage does not exist in English law, and the British royal family and British aristocracy, while traditionally concerned with rank, often adopted a far more flexible attitude than their counterparts in many Continental European countries. Queen Victoria allowed her daughter Princess Louise, Duchess of Argyll to contract an equal marriage with a non-mediatized noble (the Duke of Argyll) in 1871, which would have been completely out of the question for a member of any continental sovereign house at that time. When Elizabeth Bowes-Lyon, another non-mediatized noble, became queen consort of England in 1936 her rank wasn't an issue at all, though it would have been an insurmountable obstacle to her elevation in some European countries.
Within the British aristocracy no stigma was attached to marrying a partner from a non-noble background, provided that he or she was upper class (which in this context meant anyone from or closely allied to an aristocratic or gentry landowning family).