War of succession
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. For example, in the 10th and 11th centuries, Sassanid Persia, various states in India, the Song dynasty of China, and medieval Europe, all struggled with succession crises. According to British statesman Henry Brougham (Lord Chancellor 1830–34), there were more and longer wars of succession in Europe between 1066 and the French Revolution (1789–99) than all other wars put together. "A war of succession is the most lasting of wars. The hereditary principle keeps it in perpetual life – [whereas] a war of election is always short, and never revives", he opined, arguing for elective monarchy to solve the problem. According to Kalevi Holsti (1991, p. 308, Table 12.2), who catalogued and categorised wars from 1648 to 1989 into 24 categories of 'issues that generated wars', 'dynastic/succession claims' were (one of) the primary cause(s) of 14% of all wars during 1648–1714, 9% during 1715–1814, 3% during 1815–1914, and 0% during 1918–1941 and 1945–1989. Braumoeller (2019) attributed this drastic decrease (and practical extinction) of wars of succession from the 18th century onwards largely to the fact that 'succession no longer serves either to cement territorial holdings legitimized by continuous bloodlines or to create de facto alliances or long-standing allegiances among the Great Powers.' He added that 'an international order based on political democracy more or less eliminates the incentive for wars of royal succession.'
Wars of succession have throughout history often been the worst-case scenario for absolute monarchies and other autocracies, as they are commonly known to be at their weakest and most vulnerable when the ruler dies and it is uncertain who will be the successor. Rival claims to ultimate power within such a regime are very prone to spiralling out of control into violence, because such regimes operate according to rule by force, or might makes right. A succession crisis not only risks dragging the entire population into 'civil' war between factions backing rival pretenders, but the power vacuum it creates also presents oppressed groups within the state with an opportunity to revolt, as well as vassal states outside it to reclaim their independence, and while the state is weakened, it also provides rulers of neighbouring states the chance to invade to further their own interests (with or without their own claim to the throne, or while backing another claimant within the state). In numerous cases, the enormous long-term political and economic instability created by wars of succession caused the fall of the dynasty or the state, or both.
Scholars such as Johannes Kunisch and Johannes Burckhardt (1997) blamed wars of succession in early modern Europe on notions such as the divine right of kings and absolutism, because they created inherent problems in 'a state system that had known neither effective forms of cooperation nor a clear hierarchy that had neither experienced a formal equality between its members nor clear borders.' Nolan (2008) added about the 1650–1715 period in Europe: 'Complex issues of succession of Bourbon and Habsburg were the daily stuff of high European politics at all times, and the bane of the lives of the masses of peasants swept away by ebbing and waning tides of peace and the maelstrom of war.' To him, the Nine Years' War and (1688–1697) and War of the Spanish Succession (1701–1714) were the 'two great, climactic conflicts that submerged local conflicts', so that these decades produced 'a generation of war that swirled around the dynastic ambitions and personal convictions of Louis XIV.'

Prevention and mitigation: Throughout the centuries and across the planet, various attempts have been made at prevention or mitigation of wars of succession.

Legally fixing the order of succession (see also Orders of succession above): All over Europe (except in the Kievan Rus'), the introduction of primogeniture from the 11th to 13th century sought to establish a fixed order of succession, but it proved to be insufficient to prevent numerous succession crises and wars, as demonstrated by their persistence into the 19th century. Kokkonen and Sundell (2017) found that in Europe during 1000–1799, successions following monarchs' natural deaths considerably increased the risk of both intrastate ('civil') as well as interstate wars of succession; they calculated that monarchies practicing primogeniture did experience fewer intrastate wars than elective monarchies, but 'there is no evidence that primogeniture moderated successions' effects on interstate wars.' Luard (1992) and Duchchardt (1997) pointed out that additional diplomatic efforts such as 'offensive and defensive alliances, dynastic marriages and agreements on succession' often failed to prevent them either, although Nolan (2008) countered that the Act of Settlement 1701 (alias Act of Succession) did avoid 'another violent succession crisis upon Queen Anne's eventual death.' Modern scholars are still divided on the question whether hereditary succession (as opposed to other methods of appointing leaders) has historically been a net force for political stability, including Kokkonen and Sundell (2014), or instability, such as Steven Pinker (2011), who stated: 'The idea of basing leadership on inheritance is a recipe for endless wars of succession'. Some thinkers of the latter opinion go as far back as Thomas Paine in his pamphlet Common Sense (1776), in which his argument in favour of the American colonies in revolt against the British crown becoming a republic rather than a monarchy included his claim that hereditary succession more often than not led to civil wars.
Dividing the inheritance: A common strategy in states such as Francia and the Timurid Empire was to share the inheritance amongst male family members by giving them regional control over the realm's territory in order to appease them. One would still be the supreme ruler, while the other heirs would receive appanages and could establish cadet branches. Any landholdings and titles of princely branches that died out could be retaken by the dynasty's ruling branch. However, this division of the inheritance also granted many princes a power base from which to challenge the reigning monarch.
Abdication/delegation in favour of designated heir: Abdication of a living monarch in favour of one or more heirs was one strategy to attempt to secure a smooth transition of power. For example, Charles V, Holy Roman Emperor abdicated in 1556 and divided his possessions between his son Philip II of Spain and his brother Ferdinand I, Holy Roman Emperor before dying in 1558, splitting the House of Habsburg in a Spanish and an Austrian branch. A related strategy was a partial or gradual abdication in which the ruling monarch already delegated some of their powers to their designated heir before retiring from active politics or dying. An example is how Cosimo I de' Medici effectively retired from governing in the 1560s in favour of his son and designated successor Francesco before dying in 1574.
Eliminating potential opponents beforehand: A common set of strategies to secure one's own succession or accession or that of someone else before a war could break out was to eliminate potential rivals early on in the succession crisis, or before there even was a succession crisis. This could range from assassination to banishment, and from bodily mutilation to imprisonment. Political mutilation in Byzantine culture was one way in which rivals sought to prevent each other from staging coups d'état or wars of succession to gain the Byzantine Emperorship, either before they had the chance, or to punish them after failed attempts and to prevent future attempts. Similar mutilation of competitors for succession were also common elsewhere in Europe, such as William fitz Giroie in 11th-century Normandy. In the Ottoman Empire, succession practices against potential rival claimants ranged from committing royal fratricide to lifelong imprisonment in the Kafes. None of its succession procedures were codified, however.
Hiding the monarch's death and secretly seizing power: An ad hoc strategy that a candidate or an important player supporting a candidate might have is to try and hide the monarch's death for some time to undertake the necessary actions to secretly seize power and confront any potential rival pretenders with a fait accompli. This can only be done effectively if one can control the flow of information about the monarch's death from potential rivals.