War of succession
Terminology: 

Descriptions: In historiography and literature, a war of succession may also be referred to as a succession dispute, dynastic struggle, internecine conflict, fratricidal war, or any combination of these terms. Not all of these are necessarily describing armed conflict, however, and the dispute may be resolved without escalating into open warfare. Wars of succession are also often referred to as a civil war, when in fact it was a conflict within the royalty, or broader aristocracy, that civilians were dragged into. It depends on the circumstances whether a war of succession is also a civil war in the sense of intrastate war (if it is limited to armed conflict inside one state), or it may be an interstate war (if foreign powers intervene; sometimes called 'international' war), or both. Therefore, names or descriptions of a war may simply depend on one's perspective; for example, Nolan (2008) stated: 'The Williamite War of 1689–1691, sometimes known as the Jacobite War, was a war of succession in England and an international war for or against France for most non-Irish participants. But it was a civil war in Ireland.' Similarly, scholars sometimes disagree whether the 1657–1661 Mughal dynastic conflict (which consisted of several subconflicts, phases, and factions) should be labelled a 'war of succession' or a '(princely) rebellion'.

Orders of succession: There are several different types of orders of succession, some of which may not have been enshrined in law, but only established in local custom or tradition. Across times and places, orders of succession have switched from one system to another. Some prominent examples are:

None: Every death of a monarch results in a succession crisis that is resolved ad hoc, either diplomatically or by violence. This pattern has been observed in cultures around the world, for example in the Buyid dynasty (934–1062), Đại Cồ Việt (968–1054), Ayutthaya (17th century), and Mataram (17th–18th century).
Heir designation or selection: The reigning monarch had the sole right to personally designate his or her preferred heir while still alive, sometimes far ahead of time (perhaps already giving them important functions and dignities), sometimes only in their last will or verbally on their deathbed. This pattern has been observed in cultures around the world. For example, from Peter the Great (1721) to the Pauline Laws (1797), the Russian Empire had this system. It was also common in high medieval Mediterranean Europe to accept heir designation by will.
Co-rulership or abdication/delegation: In many states in cultures around the world, the reigning monarch gave their designated heir already a prominent role in running the realm to prevent a power vacuum upon the monarch's death, and to train the co-ruler in their future duties. The Roman Tetrarchy had two Augusti (senior emperors) and two Caesari (junior emperors, chosen by the Augusti). The Capetian kings France had their sons elected 'co-king' by his noblemen to ensure loyalty to the heir. The Han dynasty set up an Office of the Crown Prince wherein a group of officials trained and served the heir designate long ahead of the succession. In the Vietnamese Trần dynasty, the kings '[abdicated] the throne to their chosen adult heirs upon the death of their predecessors, thereafter ruling as 'senior' kings.'
Equal share within the lineage or dividing the inheritance: One son of the monarch would inherit the kingship while other sons (or other male relatives) would be given an equal share / regional control of the territory. This was common practice in Francia, and prevailed in certain regions in northern and western France such as Normandy long after the French royal dynasty had adopted primogeniture.
Agnatic seniority, collateral succession, horizontal succession, fraternal succession or brother–brother succession: When monarch X dies, his oldest brother succeeds him, and then his second-oldest brother and so on, until there are no brothers left; then, the oldest son of monarch X becomes the next monarch, and then monarch X's second-oldest son, and so on. This pattern has been observed in cultures around the world, including in many European states before the 11th century such as Piast dynasty of Poland, and the Rurik dynasty of the Kievan Rus' and its successor states), African states such as the Kanem–Bornu Empire from the 14th century onwards, or Asian states such as the Konbaung dynasty of Burma.
Patrilineal succession, vertical succession, filial succession or father–son succession: A son of the previous monarch succeeds him. There are several different subtypes of this order of succession, including:
Primogeniture: The oldest son of the previous monarch succeeds him; in case there is no son, then his eldest daughter succeeds. This system is virtually unique to Europe, and has only been adopted in very few other states in modern times.
Salic law: Only males can inherit the kingship.
semi-Salic law: Inheritance may pass through the female line but only at the extinction of all male lines.
Absolute primogeniture, gender is irrelevant and the oldest child of the last monarch automatically becomes the next ruler.
Ultimogeniture: The youngest son of the previous monarch succeeds him. This system existed in some places in medieval Europe.
Non-fixed son: There is no fixed rule which son of the previous monarch should automatically succeed him. Any son may be designated as heir by the living monarch, or be accepted by the relevant aristocrats after asserting himself through diplomacy or violence over his brothers. Examples include the Kanem–Bornu Empire until the 14th century, and Anglo-Saxon England.
Elective succession: see elective monarchy. The royal succession is decided by votes from a relatively small group of aristocrats (typically a few dozen). It may be decided by an election vivente rege ("while the king yet lives") to secure a more stable transition of power upon the monarch's death, although this was not required, and could still result in a war of succession.

Analysis: 

Common elements: A war of succession is a type of war concerning struggle for the throne: a conflict about supreme power in a monarchy. Although it is typically associated with hereditary monarchy (either with primogeniture or some other principle of hereditary succession), the concept has also been applied to elective monarchies. It may be intrastate war, an interstate war (if foreign powers intervene), or both.
A succession war may arise after (or sometimes even before) a universally recognised ruler over a certain territory passes away (sometimes without leaving behind any (legal) offspring, or failing to clearly designate an heir), or is declared insane or otherwise incapable to govern, and is deposed. Next, several pretenders (also known as 'claimants', 'candidates', or 'rivals') step forward, who are either related to the previous ruler (by ancestry or marriage) and therefore claim to have a right to their possessions based on the hereditary principle, or have concluded a treaty to that effect. They will seek allies within the nobility and/or abroad to support their claims to the throne. After all options for a diplomatic solution –such as a sharing of power, or a financial deal– or a quick elimination (in effect a coup d'état) –e.g. by assassination or arrest– have been exhausted, a military confrontation will follow. Quite often such succession disputes have led to long-lasting wars. Potential candidates were not always limited to members from the royal household; depending on circumstances, aristocrats of other noble families within the realm were eligible to replace the deceased monarch, and could seize the opportunity of a succession crisis to take control of the state and found a new dynasty.
Factors that increased the risk of a succession crisis included lack of legitimate heirs (especially when the (ruling branch of a) dynasty died out), illegitimate children, contested inheritance, and the creation of collateral dynastic branches. The last factor in particular had the potential to not only stimulate wars of succession upon a monarch's death, but also princely revolts by cadets and cousins while they were still alive. The minority of a ruler necessitated regents and ministers to run state affairs until they came of age, which made opposition from military and administrative elites to the underage monarch easier, and also increased the risk of widespread political instability and civil conflict.
Some wars of succession are about women's right to inherit. This does not exist in some countries (a "sword fief", where the Salic law applies, for example), but it does in others (a "spindle fief"). Often a ruler who has no sons, but does have one or more daughters, will try to change the succession laws so that a daughter can succeed him. Such amendments will then be declared invalid by opponents, invoking the local tradition. In Europe, the Holy Roman Emperor (or King of the Romans) increasingly regularly granted smaller inland fiefs to heirs according to the female lineage since the 13th century. The Privilegium Minus of 1156, which established the Duchy of Austria, already allowed women to inherit the state as well.

Prevalence and impact: Land inheritance disputes were frequent in agrarian societies, and the 'increasing subdivision of estates was a common cause of the undermining of territorial aristocracies' in cultures across the world.