On October 24, 1648, after thirty years of war, eight million dead, and a continent so depopulated that some German regions did not recover their prewar population for a century, the European powers signed two treaties at Münster and Osnabrück that have since been called the Peace of Westphalia. The settlement ended the wars of religion and constituted the modern state system. Sovereignty became territorial rather than confessional. Each prince's religious choice would be respected within his borders. External powers no longer had the right to intervene in another state's internal religious affairs. The era of religious universalism in European politics was over; the era of state sovereignty had begun.
What Westphalia established was less a single doctrine than a cluster of related principles that political scientists later codified as the Westphalian system: territorial sovereignty (each state has supreme authority within its borders), legal equality of states (regardless of size, the same juridical status), non-intervention in domestic affairs, and the recognition of states by other states as the basis of international legitimacy. The principles were honored as much in the breach as in the observance — eighteenth- and nineteenth-century Europe was full of partitions, interventions, and dynastic absorptions that violated them — but the normative framework held, and was extended globally as European empires collapsed in the twentieth century. The United Nations Charter (1945) is Westphalian in its core commitments: each member state has one vote in the General Assembly, sovereign equality is foundational, intervention requires Security Council authorization. The frequent twenty-first-century complaint that 'Westphalian sovereignty is breaking down' is partly accurate (humanitarian intervention, the EU's pooled sovereignty, transnational corporate power, cyberwar that ignores borders) and partly overstated (states remain the dominant political units; sovereignty remains the default starting point of international negotiation).
The Russian-Chinese rhetorical embrace of Westphalian sovereignty — non-intervention, respect for territorial integrity (selectively applied) — is now the default Global South diplomatic register, partly in opposition to a Western liberal interventionism that has eroded since the Iraq disaster. The post-2014 invasions of Ukraine and the long Israeli occupation of Palestinian territories are both, in different ways, violations of Westphalian principles by states that also invoke them. The framework remains the language of international politics even as it is regularly violated in practice; whether it survives the current strain or evolves into something else is one of the unresolved structural questions of the global order.