Monarch in the context of Regnal era

A declaration of war is a formal act by which one state announces existing or impending war activity against another. The declaration is a performative speech act (or the public signing of a document) by an authorized party of a national government, in order to create a state of war between two or more states.

The legality of who is competent to declare war varies between nations and forms of government. In many nations, that power is given to the head of state or sovereign. In other cases, something short of a full declaration of war, such as a letter of marque or a covert operation, may authorise war-like acts by privateers or mercenaries. The official international protocol for declaring war was defined in the Hague Convention (III) of 1907 on the Opening of Hostilities.

A polity is a group of people with a collective identity, who are organized by some form of political, institutionalized, social relations, and have a capacity to mobilize resources. It is the unit or entity of a political community or body politic.

A polity can be any group of people organized for governance, such as by the board of a corporation, and in the case of a federal country, the government that exists at both its federal level and the level of its subdivided regions. A polity may have various forms, such as a republic administered by an elected representative, a realm of a hereditary monarch, an incorporated city managed by an appointed mayor, and many others.

Basileus (Ancient Greek: βασιλεύς) is a Greek term and title that has signified various types of monarchs throughout history. In the English-speaking world, it is perhaps most widely understood to mean 'monarch', referring to either a 'king' or an 'emperor'. The title was used by sovereigns and other persons of authority in ancient Greece (especially during the Hellenistic period), the Byzantine emperors, and the kings of modern Greece. The name Basileios (Basil), deriving from the term basileus, is a common given name in the Eastern Orthodox Church and Syriac Orthodox Church for the Maphrian.

The feminine forms are basileia (βασίλεια), basilissa (βασίλισσα), basillis (βασιλίς), or the archaic basilinna (βασιλίννα), meaning 'queen' or 'empress'. The related term basileia (βασιλεία) has meanings such as 'sovereignty', 'royalty', 'kingdom', 'reign', 'dominion' and 'authority'.

A personal union is a combination of two or more monarchical states that have the same monarch while their boundaries, laws, and interests remain distinct. A real union, by contrast, involves the constituent states being to some extent interlinked, such as by sharing some limited governmental institutions. It differs from a federation in that each constituent state has an independent government, whereas a federal state is united by a central government. The ruler in a personal union does not need to be a hereditary monarch.

The term was coined by German jurist Johann Stephan Pütter, introducing it into Elementa iuris publici germanici (Elements of German Public Law) of 1760.

An oath of allegiance is an oath whereby a subject or citizen acknowledges a duty of allegiance and swears loyalty to a monarch or a country. In modern republics, oaths are sworn to the country in general, or to the country's constitution. For example, officials in the United States, take an oath of office that includes swearing allegiance to the United States Constitution. However, typically in a constitutional monarchy, such as in the United Kingdom, Australia, and other Commonwealth realms, oaths are sworn to the monarch. Armed forces typically require a military oath.

In feudal times, a person would also swear allegiance to their feudal superiors. To this day the oath sworn by freemen of the City of London contains an oath of obedience to the Lord Mayor of the City of London.

Archon basileus (Ancient Greek: ἄρχων βασιλεύς, árchōn basileús) was a Greek title, meaning "king magistrate"; the term is derived from the words archon "magistrate" and basileus "king" or "sovereign".

The term "high priest" usually refers either to an individual who holds the office of ruler-priest, or to one who is the head of a religious organisation.

Archon (Greek: ἄρχων, romanized: árchōn, plural: ἄρχοντες, árchontes) is a Greek word that means "ruler", frequently used as the title of a specific public office. It is the masculine present participle of the verb stem αρχ-, meaning "to be first, to rule" (see also ἀρχή "beginning, origin"), derived from the same root as words such as monarch and hierarchy.

The aristocracy (from Greek ἀριστοκρατία aristokratía, "rule of the best"; Latin: aristocratia) is historically associated with a "hereditary" or a "ruling" social class. In many states, the aristocracy included the upper class with hereditary rank and titles. They are usually below only the monarch of a country or nation in its social hierarchy.

A monarchy is a hereditary form of government in which political power is legally passed on to the family members of the monarch, a head of state who rules for life. While monarchs gain their power depending on specific succession laws, they can also gain their authority via election.

Monarchies were the most common form of government until the 20th century, when republics replaced many monarchies, notably at the end of World War I. As of 2025, forty-three sovereign nations in the world have a monarch, including fifteen Commonwealth realms that share King Charles III as their head of state. Other than that, there is a range of sub-national monarchical entities. Most of the modern monarchies are constitutional monarchies, retaining under a constitution unique legal and ceremonial roles for monarchs exercising limited or no political power, similar to heads of state in a parliamentary republic.

A parliament is the type of legislature, or law-making body, of a state based on the fusion of powers. Generally, a parliament has three functions: representing the electorate, making laws, and overseeing the executive government via hearings and inquiries. Its role is similar to that of a senate, synod or congress. The term parliament is commonly used in countries that are current or former monarchies. Some contexts restrict the use of the word to parliamentary systems, although it is also used to describe the legislature in some presidential systems (e.g., the Parliament of Ghana), even where it is not in the official name. A parliament is typically made up of elected members, who are legislators.

Historically, parliaments included various kinds of deliberative, consultative, and judicial assemblies. Parliamentary gatherings in the Middle Ages began to establish that monarchs were subject to law and first summoned representatives of common people, notably the Cortes of León in 1188 and an English parliament in 1265. During the early modern period, the Glorious Revolution of 1688 in Britain established the primacy of parliamentary sovereignty, through which the rule of law could be enforced. Many other modern concepts of parliamentary government developed subsequently in the Kingdom of Great Britain (1707–1800). Expansion of suffrage in the 19th and 20th centuries led to parliaments around the world becoming democratically elected.

Daikan (代官) was an official in ancient Japan that acted on behalf of a ruling monarch or a lord at the post they had been appointed to. Since the Middle Ages, daikan were in charge of their territory and territorial tax collection. In the Edo period, daikan were local governors in charge of the government and security of domain and shogunate territories.

An emperor (from Latin: imperator, via Old French: empereor) is the (male) ruler of an empire. Empress, the female equivalent, may indicate an emperor's wife (empress consort), mother/grandmother (empress dowager/grand empress dowager), or a woman who rules in her own right and name (empress regnant or suo jure). Emperors are generally recognized to be of the highest monarchic honour and rank, surpassing king. In Europe, the title of Emperor has been used since the Middle Ages, considered in those times equal or almost equal in dignity to that of Pope due to the latter's position as visible head of the Church and spiritual leader of the Catholic part of Western Europe. The emperor of Japan is the only currently reigning monarch whose title is translated into English as "Emperor", although he no longer reigns over an empire.

Both emperors and kings are monarchs or sovereigns, both emperor and empress are considered monarchical titles. In as much as there is a strict definition of emperor, it is that an emperor has no relations implying the superiority of any other ruler and typically rules over more than one nation. Therefore, a king might be obliged to pay tribute to another ruler, or be restrained in his actions in some unequal fashion, but an emperor should in theory be completely free of such restraints. However, monarchs heading empires have not always used the title in all contexts—the British sovereign did not assume the title Empress of the British Empire even during the incorporation of India, though she was declared Empress of India.

Sovereign immunity, or crown immunity, is a legal doctrine whereby a sovereign or state cannot commit a legal wrong and is immune from civil suit or criminal prosecution, strictly speaking in modern texts in its own courts. State immunity is a similar, stronger doctrine, that applies to foreign courts.

A parliamentary system, or parliamentary democracy, is a form of government based on the fusion of powers. In this system the head of government (chief executive) derives their democratic legitimacy from their ability to command the support ("confidence") of a majority of the parliament, to which they are held accountable. This head of government is usually, but not always, distinct from a ceremonial head of state. This is in contrast to a presidential system, which features a president who is not fully accountable to the legislature, and cannot be replaced by a simple majority vote.

Countries with parliamentary systems may be constitutional monarchies, where a monarch is the head of state while the head of government is almost always a member of parliament, or parliamentary republics, where a mostly ceremonial president is the head of state while the head of government is from the legislature. In a few countries, the head of government is also head of state but is elected by the legislature. In bicameral parliaments, the head of government is generally, though not always, a member of the lower house.

Emperor of the French (French: Empereur des Français) was the title of the monarch and supreme ruler of the First French Empire and the Second French Empire. The emperor of France was an absolute monarch.

A cadet branch consists of the male-line descendants of a monarch's, ruler's or patriarch's younger sons (cadets). In the ruling dynasties and noble families of much of Europe and Asia, the family's major assets (realm, titles, fiefs, properties, lands and income) have historically been passed from the father to his firstborn son in what is known as primogeniture; younger sons, the cadets, generally inherited less wealth and authority (such as a small appanage) to pass on to future generations of their descendants.

In families and cultures in which that was not the custom or law, such as the feudal Holy Roman Empire, the equal distribution of the family's holdings among male members was eventually apt to so fragment the inheritance as to render it too small to sustain the descendants at the socio-economic level of their forefather—and indeed, too small to efficiently manage or effectively defend. Moreover, brothers and their descendants sometimes quarreled over their allocations, or even became estranged. While agnatic primogeniture became a common way of keeping the family's wealth intact and reducing familial disputes, it did so at the expense of younger sons and their descendants. Both before and after a state legal default of inheritance by primogeniture, younger brothers sometimes vied with older brothers to be chosen as their father's heir or, after the choice was made, sought to usurp the elder's birthright.

A decree is a legal proclamation, usually issued by a head of state, judge, royal figure, or other relevant authorities, according to certain procedures. These procedures are usually defined by the constitution, Legislative laws, or customary laws of a government.