Westphalian sovereignty, or state sovereignty, is the principle of international law that each nation-state has exclusive sovereignty over its territory. External powers should not interfere in another country's domestic affairs. Each state, no matter how large or small, has equal rights to sovereignty. The principle underlies the modern international system of sovereign states. The United Nations Charter states that "nothing should authorise intervention in matters essentially within the domestic jurisdiction of any state."
The concept has been traced back to the Peace of Westphalia (1648), which ended the Thirty Years' War. The principle of non-interference was further developed in the 18th century. The Westphalian system reached its peak in the 19th and 20th centuries, as nation-states consolidated and European colonies gained their independence. After the end of the Cold War, the United States and Western Europe began talking of a post-Westphalian order in which countries could interfere against human rights abuses in other countries.  Critics have pointed out such intervention would be (and has been) used to continue processes similar to standard Euro-American colonialism, and that the colonial powers always used ideas similar to "humanitarian intervention" to justify colonialism, slavery, and similar practices. China and Russia have thus used their United Nations Security Council veto power to block American efforts to, as they see it, violate the sovereignty of other nations.
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 they 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.
The origins of Westphalian sovereignty have been traced in the scholarly literature to the Peace of Westphalia (1648). The peace treaties put an end to the Thirty Years' War, a war of religion that devastated Germany and killed 30% of its population. Since neither the Catholics nor the Protestants had won a clear victory, the peace settlement established a status quo order in which states would refrain from interfering in each other's religious practices. The principle of non-interference in other domestic affairs was laid out in the mid-18th century by Swiss jurist Emer de Vattel.
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 end of the Cold War saw increased 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.
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".
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. In a 2008 article Phil Williams links the rise of terrorism and violent non-state actors (VNSAs), which pose a threat to the Westphalian sovereignty of the state, to globalization.
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.
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, while hypocritically ignoring the same issues in other countries friendlier to the United States.
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.
The Westphalian system that developed in early modern Europe has seen its staunchest defenders in the non-Western world. The presidents of China and Russia issued a joint statement in 2001 vowing to "counter attempts to undermine the fundamental norms of the international law with the help of concepts such as 'humanitarian intervention' and 'limited sovereignty.'" China and Russia have used their United Nations Security Council veto power to block American challenges to state sovereignty in Syria. Russia was left out of the original Westphalian system in 1648, but post-Soviet Russia has seen Westphalian sovereignty as a means to balance American power by encouraging a multipolar world order.
Some in the West also speak favorably of the Westphalian state. American political scientist Stephen Walt urged U.S. President Donald Trump to return to Westphalian principles, calling it a "sensible course" for American foreign policy. American political commentator Pat Buchanan has also spoken in favor of the traditional nation-state.
But while Western governments and human rights groups welcomed enforcement of the concept of the “responsibility to protect” civilians, Moscow and Beijing did not hide their disdain for an idea they equate with violating states’ sovereignty, which the United Nations was founded to protect.