Descent is the obvious one: to be a part of a dynasty, you generally have to be descended from another member of a dynasty. For the sake of most of my research, you have to be descended from another male of the dynasty, through another male of the dynasty. Thus Edward -> John -> Henry would be a descent, or Edward -> John -> Elizabeth would be a descent. Again, think of surnames. They are important. In the previous example, add in the surname Plantagenet and you have the descent of two members of the British royal family circa 1400: Edward III Plantagent -> John Plantagenet, Duke of Lancaster -> Elizabeth, Duchess of Exeter. See how they all have the same surname? It is just like modern times. Many dynasties, especially those before the 1800s, didn't adopt formal surnames but other patterns developed to help trace lineage. For women it can be easy, just see what they were known by: Marie of France is probably a French princess. Men can be a bit harder, but for upper royalty they still often have predictable titles such as Duke of Berri, Duke of Orléans. They may take more work to realize, but the patterns are still there.
Marriage is the other important aspect of dynasties. Remember that in most western culture since early Medieval times or before, women were commodities. I know, nothing anyone wants to hear, but it has much truth to it. In our modern times, when a couple get married they get engaged, have a wedding, and then move in together (or something close to that). In medieval times, royalty and nobility generally were betrothed, often at a young age, and the woman moved in with the man when the she was old enough to have sex, about the age of 13 or so depending on the region. They may not have a formal wedding for years or not at all; the betrothal was in all essence the wedding and it required very little pomp. The marriage was strictly a public exercise to make the couple legitimate to the public and to place them in the public (church) record. Children of betrothed people were considered legitimate in the church's eyes even without a wedding ceremony. When the wife married a man, she became a de facto member of his dynasty. In many cases, she would even take on his surname, which in medieval times was generally "of" someplace. Thus, Marie of France may confusingly also be an English princess who married a French royal. While she generally retained her rights as a member of her birth dynasty, her status basically shifted to that of her husband. The reverse was almost never true: husbands rarely became members of their wife's dynasties. The only exception was when a prominent woman wed someone of lesser stature and it is often done through official decree. Queen Maria Theresa of Austria in 1740 proclaimed her children Habsburgs despite the fact that her husband was of the House of Lorraine; she continued her dynasty despite a technical dynastic shift. Queen Elizabeth II of the United Kingdom did a similar thing when she wed Philip of Greece, a member of the House of Oldenburg. Her dynasty, the House of Windsor, should end when she dies, but it will continue under formal decree. Thus a woman can bring a husband into her dynasty, but it is generally rare. Nobility are known to do it much more frequently, however.
With those terms under control, lets move on to the last subject for today: succession. Succession in dynastology is when one person inherits, conquers, or marries into the position of a predecessor. To be a monarch or noble, you pretty much have to succeed someone else unless you are the founder (or refounder). It should seem pretty simple but it is very much not. Dynastic succession is in fact one of the most difficult things to do and, depending on the importance and/or questionableness of the succession, can lead to warfare. Indeed, virtually every type of succession has led to a succession war. Here are the major forms of dynastic succession in Europe historically:
- Male-preference Cognatic Primogeniture — This is the most standard format practiced in Europe even today. Basically, a monarch has children, boys and girls. When they die, their eldest son inherits everything and the others are left under the care of their elder brother or their spouses (or military careers or religious organizations, &c.). If that son dies without issue (children), then the next-eldest brother inherits. If there are no other brothers, then the eldest daughter inherits, &c. In most cases, it doesn't come to all that. Most of the time, a son is either born to the dynast or one of his brothers. Dynastic shifts, though, are much more common in this form of succession because if a dynast only has daughters, they inherit before any brothers. This happened with Queen Victoria, the daughter of Edward of Kent. Edward had a younger brother, Ernest, but his daughter had precedence over him. The majority of succession wars occur because this form of succession leaves open problems when you have to go back multiple generations looking for the closest-related cousin.
— Suo Uxoris Primogeniture — I place this as a subset of the previous because it really is no different in function, just the result. In normal male-preference primogeniture, the woman is the legal heir and successor in cases of female succession. In suo uxoris, the husband of the heiress inherits the titles while the woman just happily strolls on with her life. This was the case with Juana of Spain who, when she became Queen of Castile in 1504, gave her rights to her husband who became Philip I of Castile suo uxoris ("in right of his wife").
- Salic Law — Salic law is often also called agnatic primogeniture. It is a very specific type of descent quite different than the previous. The Salic Law was probably established by the Salian Franks in the 600s or earlier. It stated that a dynast must be a male in the male line; a male who passes through a female has no rights. Thus, even though King Henry III had a surviving sister (which he did), his distant cousin Henry III of Navarre was his heir because the French practiced Salic Law (as did most of Germany). The Wars of Religion in France was partly due to the fact that a Protestant (Henry of Navarre) was heir to the Catholic throne of France.
—Partible Inheritance — Quite possibly the most annoying and destructive form of succession in terms of posterity, this method usually follows Salic Law but instead of granting the entire inheritance to the eldest son, it grants it equally to all the sons. Thus the Duchy of Saxony becomes Saxe-Gotha, Saxe-Coburg, the Electorate of Saxony, &. It often takes generations, if it happens at all, for all the lines to die off allowing one dynast to once again rule the entire hereditary land. Management of these realms is often as confusing, but luckily outside the scope of dynastology (although not dynastic politics).
- Proximity of Blood — With proximity of blood, you start getting into dangerous grounds. It is basically what it sounds like: whoever is most closely related to you gets the title. In reality, it is chaos and one of the reasons why proper care must be kept in maintaining the other forms of succession. If one form of succession breaks down, Proximity of Blood takes over. It basically works like this: King Charles IV of France dies. France has not yet established formally how they want to handle difficult successions but tradition established the Salic Law, thus Philip VI of Valois, his father's brother's son, becomes king. The only problem is that Edward III of England is the son of Isabella, Charles IV's sister. Edward claims that he is closer in proximity of blood to Charles because he is Charles' nephew rather than his first cousin. The result: the Hundred Years War. THAT is why proximity of blood doesn't work.
- Tanistry — This old law was most dysfunctional, hence why it went away. It argued that the most senior member of a dynasty should rule, regardless of descent. That means that you have King Kenneth I of Scotland who has two sons. When the first son dies, his brother becomes king despite the fact that the first son has a son. When that son dies, the first son's son becomes king. When he dies, the second son's son becomes king. You can probably guess how confusing this gets when kings have multiple sons that have multiple sons. It's really not that pretty and it took Malcolm III a lot of courage to overthrow this old system in Scotland. The war between Macbeth and Duncan I was based mostly on the ambiguity of this system.
- Election — It is not unheard of that monarchs be elected. This was especially common in the Holy Roman Empire and the late period of the Kingdom of Poland, and is still practiced by the Papacy today. Basically, a council of nobles chosen from the land come together and choose their leader. There may or may not be any prerequisites, although the elect is often the heir of the predecessor. While the candidates may still inherit and do what they will with their hereditary lands, the elective title must be conferred by the nobles and generally cannot be claimed without that support. A civil war in the 1200s was fought between three rival Holy Roman Emperors (all received an inadequate number of votes by the Electoral College) until Rudolf I of Austria defeated them all and was elected sole emperor.
- Equal Cognative Primogeniture — This is obviously a spin-off of the first item on this list, but it deserves its own place. This is quickly becoming the popular form of succession among European royals. Tradition has always placed the men in the front of the line of succession, but Scandinavian and Low Country royalty have almost all adopted equal primogeniture, now, meaning that the eldest child, regardless of sex, inherits the title. That means that Victoria of Sweden is first in line to the throne despite the existence of her younger brother, Carl Philip (who was bumped in 1980 when he was just an infant). This practice has never really been mainstream until 1980.