State sovereignty is the principle of international law that each nation-state has sovereignty over its territory and domestic affairs, to the exclusion of all external powers, on the principle of non-interference in another country's domestic affairs, and that each state (no matter how large or small) is equal in international law. As European influence spread across the globe, these principles became central to international law and to the prevailing world order.
The principle of sovereignty thus underlies the modern international system of states. The origins of this system are often traced in scholarly and popular literature to the Peace of Westphalia, signed in 1648, which ended the Thirty Years' War. However, both the basis and the conclusion of this view have been criticized by some revisionist academics and politicians, with revisionists questioning the significance of the Peace, and some commentators and politicians attacking the Westphalian system of sovereign nation-states.
The traditional view of the Westphalian system is that the Peace of Westphalia was an agreement to respect the principle of territorial integrity. In the Westphalian system, the national interests and goals of states (and later nation-states) were widely assumed to go beyond those of any citizen or any ruler. States became the primary institutional agents in an interstate system of relations. The Peace of Westphalia is said to have ended attempts to impose supranational authority on European states. The "Westphalian" doctrine of states as independent agents was bolstered by the rise in 19th century thought of nationalism, under which legitimate states were assumed to correspond to nations—groups of people united by language and culture.
The Westphalian system reached its peak in the late 19th century. Although practical considerations still led powerful states to seek to influence the affairs of others, forcible intervention by one country in the domestic affairs of another was less frequent between 1850 and 1900 than in most previous and subsequent periods.
The Peace of Westphalia is important in modern international relations theory, and is often defined as the beginning of the international system with which the discipline deals.  However, recent scholarship suggests that the Westphalian treaties actually had little to do with the principles -- i.e., sovereignty, non-intervention, and the legal equality of states -- with which the treaties are often associated. For example, Osiander writes that "[t]he treaties confirm neither [France's or Sweden's] 'sovereignty' nor anybody else's; least of all do they contain anything about sovereignty as a principle."
Nonetheless, 'Westphalian sovereignty' continues to be used as a shorthand for some of the basic legal principles underlying the modern state system. The applicability and relevance of these principles have been questioned from the mid-20th century onward from a variety of viewpoints. Much of the debate has turned on the ideas of internationalism and globalization which, in various interpretations, appear to conflict with Westphalian sovereignty.
In 1998, at a Symposium on the Continuing Political Relevance of the Peace of Westphalia, NATO Secretary-General Javier Solana said that "humanity and democracy [were] two principles essentially irrelevant to the original Westphalian order" and levied a criticism that "the Westphalian system had its limits. For one, the principle of sovereignty it relied on also produced the basis for rivalry, not community of states; exclusion, not integration."
In 1999, British Prime Minister Tony Blair gave a speech in Chicago where he "set out a new, post-Westphalian, 'doctrine of the international community.'" Blair argued that globalization had made the Westphalian approach anachronistic. Blair was later referred to by The Daily Telegraph as "the man who ushered in the post-Westphalian era." Others have also asserted that globalization has superseded the Westphalian system.
In 2000, Germany's Foreign Minister Joschka Fischer referred to the Peace of Westphalia in his Humboldt Speech, which argued that the system of European politics set up by Westphalia was obsolete: "The core of the concept of Europe after 1945 was and still is a rejection of the European balance-of-power principle and the hegemonic ambitions of individual states that had emerged following the Peace of Westphalia in 1648, a rejection which took the form of closer meshing of vital interests and the transfer of nation-state sovereign rights to supranational European institutions."
In the aftermath of the 11 March 2004 Madrid attacks, Lewis 'Atiyyatullah, who claims to represent the terrorist network al-Qaeda, declared that "the international system built up by the West since the Treaty of Westphalia will collapse; and a new international system will rise under the leadership of a mighty Islamic state".
Others speak favorably of the Westphalian state, notably European nationalists and American paleoconservative Pat Buchanan. Some such supporters of the Westphalian state oppose socialism and some forms of capitalism for undermining the nation state. A major theme of Buchanan's political career, for example, has been attacking globalization, critical theory, neoconservatism, and other philosophies he considers detrimental to today's Western nations.
During the 1980s and early 1990s, the imperative of globalization and interdependence led to international integration, and, arguably, the erosion of Westphalian sovereignty. Much of the literature was primarily concerned with criticizing realist models of international politics in which the notion of the state as a unitary agent is taken as axiomatic.
The European Union's concept of shared sovereignty is also somewhat contrary to historical views of Westphalian sovereignty, as it provides for external agents to influence and interfere in the internal affairs of its member countries.
Since the late 20th century, the idea of Westphalian sovereignty has been brought into further question by a range of actual and proposed military interventions in the former Yugoslavia, Afghanistan, Iraq, Libya, Sudan, Vietnam and Crimea, among others.
Interventions such as in Cambodia by Vietnam (the Cambodian–Vietnamese War) or in Bangladesh (then a part of Pakistan) by India (the Bangladesh Liberation War and the Indo-Pakistani War of 1971) were seen by some as examples of humanitarian intervention, although their basis in international law is debatable.
Other more recent interventions, and their attendant infringements of state sovereignty, also have prompted debates about their legality and motivations.
Such interventions include:
A new notion of contingent sovereignty seems to be emerging, but it has not yet reached the point of international legitimacy. Neoconservatism in particular has developed this line of thinking further, asserting that a lack of democracy may foreshadow future humanitarian crises, or that democracy itself constitutes a human right, and therefore nation states not respecting democratic principles open themselves up to just war by other countries. However, proponents of this theory have been accused of being concerned about democracy, human rights and humanitarian crises only in countries where American global dominance is challenged, such as the former Yugoslavia, Iraq, Iran, Russia, China, Belarus, North Korea, Sudan, Venezuela, etc., while hypocritically ignoring the same issues in other countries friendlier to the United States, such as Pakistan, Saudi Arabia, the United Arab Emirates, Jordan, Egypt, Georgia, and Colombia.
Further criticism of Westphalian sovereignty arises regarding allegedly failed states, of which Afghanistan (before the 2001 US-led invasion) is often considered an example. In this case, it is argued that no sovereignty exists and that international intervention is justified on humanitarian grounds and by the threats posed by failed states to neighboring countries and the world as a whole.