Universal monarchy

A universal monarchy is a concept and political situation where one monarchy is deemed to have either sole rule over everywhere (or at least the predominant part of a geopolitical area or areas) or to have a special supremacy over all other states (or at least all the states in a geopolitical area or areas).
Concept.
Universal monarchy is differentiated from ordinary monarchy in that a universal monarchy is beholden to no other state and asserts a degree of total sovereignty over an area, or predominance over other states.
The concept has arisen in Europe and Asia. The concept is linked to that of Empire, but implies more than simply possessing "imperium".
The Latin phrase "Dominus Mundi", Lord of the World, encapsulates the concept. Though in practice no universal monarchy, or indeed any state, ever held rule over the whole world, it may have appeared to many people, particularly pre-modern, that it did.
Critical of the concept in Europe in the Middle Ages were philosophers such as Nicole Oresme and Erasmus; whereas Dante and Guillaume Postel were more favourable. Later, Protestants would seek to reject the concept, identifying it with Catholicism.
History.
Europe.
In Europe the expression of a Universal Monarchy as actual total "imperium" can be seen in the Roman Empire, and as the predominate ‘sole sovereign’ state during its Byzantine period, where the Emperor by virtue of being the head of Christendom claimed a sovereignty over all other kings even though in practice this could not be enforced. The Byzantine conception went through two phases, initially as expounded by Eusebius that just as there was one God so there could only be one Emperor, which developed in the 10th century into the conception of the Emperor as the "paterfamilias" of a family of kings who were the other rulers in the world. Such concepts were a feature of the Ottoman Empire successor state, particularly when military rule was augmented by the Caliphate.
The idea of a sole sovereign Emperor would re-emerge in the West with Charlemagne and the Holy Roman Empire. The idea of the Holy Roman Empire possessing a special sovereignty as a Universal Monarchy was respected by the surrounding powers and subject states, even when that Empire had undergone severe fragmentation. The symbolism of the "All the world is subject to Austria" (A.E.I.O.U.) phrase of Frederick III can be seen as an expression of the idea of all states being subject to one monarchy.
Charles V’s empire, encompassing much of western Europe and the Americas “was the nearest the post-classical world would come to seeing a truly world-wide monarchy, and hence the closest approximation to universal imperium” since the Roman Empire. It was envisaged by its supporters as a world empire that could be religiously inclusive.
Subsequently, the idea of a Universal Monarchy based on predominance rather than actual total rule would become synonymous with France attempting to establish hegemony over western Europe, particularly under Louis XIV, exemplified by the concept of Louis XIV as the 'Sun King' around which all the other monarchs became subordinate satellites. In 1755, during the reign of Louis XIV's successor Louis XV, Duke Adrien Maurice de Noailles, a member of the Council of State and formerly a key foreign policy advisor to the king, warned of a British challenge for "the first rank in Europe" through the domination of Atlantic commerce. Noailles wrote "However chimerical the project of universal monarchy might be, that of a universal influence by means of wealth would cease to be a chimera if a nation succeeded in making itself sole mistress of the trade of America."
Universal Monarchy would flourish at either end of Europe, in Britain and Russia. The Russian Universal Monarchy was Orthodox, autocratic and possessed a vast contiguous empire throughout Europe and Asia and can be seen to have similarities and differences with Byzantine rule. The British Universal Monarchy was “Protestant, commercial, maritime and free” and was not composed of contiguous territory. It had both similarities and difference with the Spanish Empire. Whereas Catholicism provided ideological unity for the Spanish Empire, British Protestant diversity would lead to “disunity rather than unity”. It was only later that federalism and economic control was seen as a means to provide unity where religious diversity could not, as with the idea of Imperial Federation as promoted by Joseph Chamberlain.
Napoleon came close to creating something akin to a Universal Monarchy with his continental system and Napoleonic Code, but he failed to conquer all of Europe. The last attempt to create a European Universal Monarchy was that attempted by Imperial Germany in World War I. If Germany had been victorious, the German Kaiser would have been suzerain over most of Europe.
Asia.
A parallel process occurred in Asia. Whereas in the West the title of Emperor had by the 19th century largely been stripped of religious connotations and had come to be seen purely in political terms, the title in eastern Asia is almost entirely a religious one, commonly stated as "The Son of Heaven". Here the title denotes a higher, "heavenly" rule ("celestial empire"), in contrast to kings who rule between heaven and earth, and by extension today to presidents who are mere base earthly rulers. Imperial China was regarded by its citizens as a Universal Monarchy where all other monarchs were regarded as tributary; this was exemplified in the Chinese name for the state which survives to this day, "Zhongguo", meaning "Middle/Central Kingdom". The concept was taken up by the Mongols, who under Genghis Khan were able to enforce this concept more widely than China. The Japanese attempt to unify South East Asia in the Greater East Asia Co-Prosperity Sphere under the Shōwa emperor follows the model set by Imperial Germany and Joseph Chamberlain of imperial rule based on economic union, matched with Japanese religious ideas.
The Hindu/Buddhist concept of the Chakravartin is a perfect illustration of the ideal of a Universal Monarch.