The very next year 1916, saw another change of name as the YMPCA became Junior Citizens, commonly called JCs, which later became Jaycees. During World War I the JCs formed Company "L" of the 138th infantry regiment. The commander was Dwight Davis who later became assistant secretary of war and donated the Davis Cup Tennis Trophy.

The year 1918 marked another change as the JCs was affiliated to the St. Louis Chamber of Commerce and officially became the St, Louis Junior Chamber of Commerce.

After World War I, Giessenbier contacted other cities in the United State with similar young businessmen's groups and subsequently 29 clubs from around the nation formed The United State Junior Chamber of Commerce. Henry "HY" Giessenbier was elected the first President of the National Organization.

The international Local Organisation of the organization began in 1923 with the Winnipeg Board of Trade's becoming the first Junior Chamber outside the United States. By 1928 the idea of an international body crossed the Atlantic Ocean to England.

In 1940 a resolution was passed by the United State Junior Chamber approving a program to further mutual interest among countries in Central and South America. This lead to the establishment of Junior Chamber in Mexico City, El Salvador, Honduras, Nicaragua, Costa Rica and Panama City in 1943.

The realization of Junior Chamber International had begun. In December 11 1944, first International Conference was held in Mexico City. Raul Garcia Vidal of Mexico was elected the first President. The countries which formed Junior Chamber International were: Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama and the United State of America.

Junior Chamber International has grown to nearly half-a-million members between the ages of 18 and 40 in more than 125 countries and over 5,000 communities around the world today.