The Treaty of Westphalia in 1648 established the modern state system and ended the Thirty Years War.
The Treaty of Westphalia, signed in 1648, resulted in the establishment of the modern state system and the end of the Thirty Years War. This treaty marked the onset of modern international law and diplomacy and solidified the notion of sovereignty of states over their own affairs, especially in northern Protestant principalities of Germany and the Holy Roman Empire.
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