What was the first international attempt to put liberal theory into practice?

Question

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The Concert of Europe, established after the Napoleonic Wars during the Congress of Vienna in 1815, was the first significant attempt to manage international affairs through a cooperative agreement between the major powers, aiming to maintain the balance of power and prevent the outbreak of further widespread conflict. This aligns with liberal theory, which emphasizes international cooperation and the establishment of international norms and institutions to preserve peace.

What Was the First International Attempt to Put Liberal Theory