The ITU is the oldest international organization, preceded by the now defunct International Telegraph Union which drafted the earliest international standards and regulations governing international telegraph networks. 

ITU headquarters

The development of the telegraph in the early 19th century changed the way people communicated on the local and international levels. Between 1849 and 1865, a series of bilateral and regional agreements among Western European states attempted to standardize international communications.

By 1865 it was agreed that a comprehensive agreement was needed in order to create a framework that would standardize telegraphy equipment, set uniform operating instructions, and lay down common international tariff and accounting rules. Between 1 March and 17 May 1865, the French Government hosted delegations from 20 European states at the first International Telegraph Conference in Paris.

The first Convention of the International Telegraph Union signed in 1865

This meeting culminated in the International Telegraph Convention which was signed on 17 May 1865. As a result of the 1865 Conference, the International Telegraph Union, the predecessor to the modern ITU, was founded as the first international standards organization.

International 'Telegraph' Union changed to 'Telecommunication' in 1932 as tech evolves

The Union was tasked with implementing basic principles for international telegraphy. This included: the use of the Morse code as the international telegraph alphabet, the protection of the secrecy of correspondence, and the right of everybody to use the international telegraphy

The ITU coordinates the shared global use of the readio spectrum, promotes international cooperation in assigning satellite orbits, works to improve telecommunication infrastructure in the developing world, and assists in the development and coordination of worldwide technical standards.

ITU Monument

The ITU is also active in the areas of broadband Internet, latest-generation wireless technologies, aeronautical and maritime navigation, radio astronomy, satellite-based meteorology, convergence in fixed-mobile phone, Internet access, data, voice, TV broadcasting, and next-generation networks.

According to en.wikipedia