War of succession
By contrast, rulers of the later Trần dynasty (1225–1400) had adopted the practice of "[abdicating] the throne to their chosen adult heirs upon the death of their predecessors, thereafter ruling as 'senior' kings." Tarling added that "the Tran kings made decisions in consultation with their uncles, brothers, and cousins, thereby fostering solidarity within the royal clan", and that the dynasty began to collapse when these rules were no longer observed. When the childless king Trần Dụ Tông failed to designate an heir, his death in 1369 marked the beginning of two decades of succession-based warfare, until prime minister Hồ Quý Ly seized power and restored order in 1390, and abolished the Tran dynasty in favour of his own in 1400.

Siam/Thailand: With the exception of Naresuan's succession by Ekathotsarot in 1605, "the method of royal succession at Ayutthaya throughout the seventeenth century was battle." Although European visitors to Thailand at the time tried to discern any rules in the Siamese order of succession, noting that in practice the dead king's younger brother often succeeded him, this custom appears not to have been legally enshrined anywhere. The ruling king did often bestow the title of uparaja ('viceroy') upon his preferred successor, but in reality, it was an "elimination process": any male member of the royal clan (usually the late king's brothers and sons) could claim the throne of Ayutthaya for himself, and win by defeating all his rivals. Moreover, groupings of nobles, foreign merchants, and foreign mercenaries actively rallied behind their preferred candidates in hopes of benefiting from each war's outcome.

European patterns: 

Causes: The origins of wars of succession in Europe lie in feudal or absolutist systems of government, in which the decisions on war and peace could be made by a single sovereign without the population's consent. The politics of the respective rulers was mainly driven by dynastic interests. German historian Johannes Kunisch (1937–2015) ascertained: "The all-driving power was the dynasties' law of the prestige of power, the expansion of power, and the desire to maintain themselves." Moreover, the legal and political coherence of the various provinces of a "state territory" often consisted merely in nothing more than having a common ruler (a personal union). Early government systems were therefore based on dynasties, the extinction of which immediately brought on a state crisis. The composition of the governmental institutions of the various provinces and territories also eased their partitioning in case of a conflict, just like the status of claims on individual parts of the country by foreign monarchs.
Early medieval Europe was rife with conflicts over property or property rights. R. I. Moore (2000) characterised the situation as "apparently endless and pointless internecine conflict which raged at every level of aristocratic society from the tenth century onwards. It continued everywhere in Latin Europe (though taking a somewhat different form to the east of the Rhine) throughout the eleventh century, and did not subside in most regions until well into the twelfth." Usually, a designated or prospective heir to a property (typically but not always the owner's oldest son) would face off demands by uncles and brothers, aunts and sisters (often represented by their husbands) and their children to grant them a fair share in the inheritance. Moore stated: "Title to landed property would always remain a source of endless and bitter contention, governed by infinitely various and complicated combinations of differing legal traditions and local customs and conditions."

Justifications: To wage a war, a justification is needed (Jus ad bellum). These arguments may be put forward in a declaration of war, to indicate that one is justly taking up arms. As the Dutch lawyer Hugo Grotius (1583–1645) noted, these must make clear that one is unable to pursue their rightful claims in any other way. The claims to legal titles from the dynastic sphere were a strong reason for war, because international relations primarily consisted of inheritance and marriage policies until the end of the Ancien Régime. These were often so intertwined that it had to lead to conflict. Treaties that led to hereditary linkages, pawning and transfers made various relations more complicated, and could be utilised for claims as well. That claims were made at all is due to the permanent struggle for competition and prestige between the respective ruling houses. On top of that came the urge of contemporary princes to achieve "glory" for themselves.

Prince-bishoprics: In some cases, wars of succession in Europe could also be centred around the reign in prince-bishoprics. Although these were formally elective monarchies without hereditary succession, the election of the prince-bishop could be strongly intertwined with the dynastic interests of the noble families involved, each of whom would put forward their own candidates. In case of disagreement over the election result, waging war was a possible way of settling the conflict. In the Holy Roman Empire, such wars were known as diocesan feuds.

Primogeniture and international law: After numerous familial conflicts, the principle of male primogeniture originated in Western Europe in the 11th century, spreading to the rest of Europe (with the exception of Kievan Rus' and subsequent Rus' principalities) in the 12th and 13th century; it has never been widely adopted outside Europe. This restricted the number of potential heirs to the oldest son of the reigning monarch, thereby facilitating undivided inheritance and a great reduction of potential sources of property conflict. Another major effect of the near-universal introduction of male primogeniture was the strengthening of patrilineality, and the structural undermining and destruction of the women's property rights, be they mothers, wives or daughters. For example, women in northern Italy, who had the ancient right to inherit a tercia, one third of their husband's estate, lost it in the 12th century (Genoa: 1143).
However, it did not prevent the outbreak of wars of succession altogether. A true deluge of succession wars occurred in Europe between the Thirty Years' War (1618–1648) and the Coalition Wars (1792–1815). According to German historian Heinz Duchhardt (1943) the outbreak of wars of succession in the early modern period was stimulated on the one hand by the uncertainty about the degree to which regulations and agreements on hereditary succession were to be considered a respectable part of emerging international law. On the other hand, there was also a lack of effective means to provide them recognition and validation. Jeroen Duindam (2021) noted that, 'when the internal challenges to dynastic supremacy had abated' in 17th- and 18th-century Europe, the royal courts forged more and more marriages alliances with the ruling houses of other sovereign states, which 'helps to explain the prevalence of international wars of succession' in that period.
Wars of succession in Europe gradually came to an end in the 19th century, when absolute monarchies were replaced by an international order based on democracy, featuring constitutional monarchies or republics.

List of wars of succession: 

In popular culture: Wars of Succession, a 2018 strategy video game developed by AGEod about the War of the Spanish Succession (1701–1714) and the Great Northern War (1700–1721), most of which focused around the succession of Poland.
Age of Empires IV, a 2021 strategy video game developed by Relic Entertainment, features a campaign that includes William the Conqueror's Norman Conquest (1066–1075) as well as the Rebellion of 1088, a war of succession between William's sons upon his death.

In fiction: In J.R.R. Tolkien's fantasy world of Middle-earth (developed 1937–1973), several wars of succession take place, such as:
The Wars with Angmar (T.A. 861–1975), after King Eärendur of Arnor died in T.A. 861 and the kingdom was split between his three quarreling sons, founding the rival realms of Arthedain, Cardolan and Rhudaur. When the lines of Eärendur died out in Cardolan and Rhudaur, King Argeleb I of Arthedain intended to reunite Arnor in T.A. 1349 and was recognised by Cardolan, but then the Witch-king of Angmar intervened, annexed Rhudaur, ravaged Cardolan and besieged Arthedain's capital city of Fornost. In T.A. 1973–1975, Arthedain was finally destroyed; even though allied Men from Gondor and Elves from Lindon subsequently succeeded in defeating Angmar in the Battle of Fornost and driving out the Witch-king, the Kingdom of Arnor would never be restored until the dawn of the Fourth Age by Aragorn.
The Succession Wars (1980), a wargame set in the BattleTech universe
The Successions, civil wars over the monarchy of Andor in The Wheel of Time (1990–2013)
The books in George R.R. Martin's A Song of Ice and Fire series (1996–) and its TV adaptation, Game of Thrones feature the War of the Five Kings, based around five individuals declaring themselves king, three of whom compete over the Iron Throne (A Song of Ice and Fire) after the death of King Robert Baratheon.