An excerpt from the Stanford Encyclopedia entry on Sovereignty.
Over the past half millennium, these claims have taken extraordinarily diverse forms — nations asserting independence from mother states, communists seeking freedom from colonialists, the vox populi contending with ancien regimes, theocracies who reject the authority of secular states, and sundry others. It is indeed a mark of the resilience and flexibility of the sovereign state that it has accommodated such diverse sorts of authority. Though a catalog of these authorities is not possible here, three dimensions along which they may be understood will help to categorize them: the holders of sovereignty, the absolute or non-absolute nature of sovereignty, and the relationship between the internal and external dimensions of sovereignty.
As suggested, diverse authorities have held sovereignty — kings, dictators, peoples ruling through constitutions, and the like. The character of the holder of supreme authority within a territory is probably the most important dimension of sovereignty. In early modern times, French theorist Jean Bodin thought that sovereignty must reside in a single individual. Both he and English philosopher Thomas Hobbes conceived the sovereign as being above the law. Later thinkers differed, coming to envision new loci for sovereignty, but remaining committed to the principle.
Sovereignty can also be absolute or non-absolute. How is it possible that sovereignty might be non-absolute if it is also supreme? After all, scholars like Alan James argue that sovereignty can only be either present or absent, and cannot exist partially (James 1999, 462–4). But here, absoluteness refers not to the extent or character of sovereignty, which must always be supreme, but rather to the scope of matters over which a holder of authority is sovereign. Bodin and Hobbes envisioned sovereignty as absolute, extending to all matters within the territory, unconditionally. It is possible for an authority to be sovereign over some matters within a territory, but not all. Today, many European Union (EU) member states exhibit non-absoluteness. They are sovereign in governing defense, but not in governing their currencies, trade policies, and many social welfare policies, which they administer in cooperation with EU authorities as set forth in EU law. Absolute sovereignty is quintessential modern sovereignty. But in recent decades, it has begun to be circumscribed by institutions like the EU, the UN’s practices of sanctioning intervention, and the international criminal court.
A final pair of adjectives that define sovereignty is “internal” and “external.” In this case, the words do not describe exclusive sorts of sovereignty, but different aspects of sovereignty that are coexistent and omnipresent. Sovereign authority is exercised within borders, but also, by definition, with respect to outsiders, who may not interfere with the sovereign’s governance. The state has been the chief holder of external sovereignty since the Peace of Westphalia in 1648, after which interference in other states’ governing prerogatives became illegitimate. The concept of sovereignty in international law most often connotes external sovereignty. Alan James similarly conceives of external sovereignty as constitutional independence — a state’s freedom from outside influence upon its basic prerogatives (James 1999, 460–462). Significantly, external sovereignty depends on recognition by outsiders. To states, this recognition is what a no-trespassing law is to private property — a set of mutual understandings that give property, or the state, immunity from outside interference. It is also external sovereignty that establishes the basic condition of international relations — anarchy, meaning the lack of a higher authority that makes claims on lower authorities. An assemblage of states, both internally and externally sovereign, makes up an international system, where sovereign entities ally, trade, make war, and make peace.