Model UN began as a series of student-led Model League of Nations simulations. It is believed that the first Model League of Nations conferences were held in the 1920s, before transitioning to Model UN after the formation of the League’s successor organization, the United Nations, in 1945. Today, some Model United Nations conferences include simulations of the League of Nations among their committee offerings.
The first Model United Nations was held at St. Lawrence University from 11–13 February 1949.It was initiated by Dr. Harry Reiff, Head of the History and Government Department, with the assistance of departmental colleague Otto L. George. Dr. Reiff was a technical advisor on the United States delegation to the 1945 San Francisco Conference (where the UN Charter was written) and the UN Organizational Conference in London in 1945-46 (where the UN was established). The 1949 St. Lawrence University Model UN conference included delegates from regional conferences and universities, including Adelphi, Alfred, Champlain, Clarkson, McGill, Middlebury, Potsdam, St. Michael’s, and Vermont. The conference continued annually for many years at St. Lawrence and has recently been revived on the campus. Other Model UN conference were developed later at Berkeley, Harvard and the National Model United Nations Harvard Model United Nations (HMUN), and National Model United Nations (NMUN NY) as well as many other colleges and universities.
In 1987, a few American exchange students founded TEIMUN in The Hague. In recent decades, Model UN has spread to East and South Asia, the Middle East, Europe, North Africa, and sub-Saharan Africa. Other major conference organizers such as Indian International Model United Nations, Harvard, THIMUN establishing additional conferences in these regions to meet burgeoning demand. The Ivy League Model United Nations, an arm of the Model UN at the University of Pennsylvania, hosts conferences for high-school-aged delegates in India and China, as well.
source : https://en.wikipedia.org/wiki/Model_United_Nations