What year was the multilateral diplomacy?

Multilateral diplomacy as a formal practice began to take shape after World War I, particularly with the establishment of the League of Nations in 1920. However, its principles and practices have evolved over centuries, influenced by earlier diplomatic efforts and treaties. The concept became more prominent in the post-World War II era with the founding of the United Nations in 1945, which institutionalized multilateral diplomatic efforts on a global scale.