Further gradations could be made: Blackstone distinguished within the nobility the degrees of the peerage, and within the commonalty knights, esquires, gentlemen, tradesmen, artificers and laborers; but ultimately, in English law, the only distinction that really mattered was that between peers and commoners.
In German society, these distinctions mattered quite a bit more than in England.
The families derived these rules partly in common, partly independently of each other.
I then consider in turn separately unequal marriages and mismarriages through examples (3) and then turn to a general discussion (4) and examples (5) of morganatic marriages.
An appendix provides examples of equality requirements in house laws, another appendix lists the marriages mentioned in this page in chronological order, and the bibliography is organized by topic. most European monarchies have adopted various rules controlling whom their dynasts could marry and how.
Until 1806, inside the area of Germany (or the Holy Roman Empire) there existed a large number of more or less autonomous dynasties, under the nominal lordship of an elected monarch (the Emperor).
They were much more powerful than titled nobles in other countries, while not quite achieving full-fledged independence and sovereignty.
This well-known feature (although restricted in 1356 in the case of electorates) led to fragmentation of estates and principalities over time.
Dynasties striving to maintain size and coherence fought over time against the strength of this general norm, and against the competing demands of younger siblings, looking for ways to curb this fragmentation.
They have in common that, in almost all cases, they were written rules edicted by a sovereign.
Concerning these marriage rules, Germany's history is unique for several reasons.
The approach I take is legal-historical: I want to understand these concepts as legal concepts in their historical context. The rest of this introduction provides the context for unequal marriages in European dynasties and in German society.