Which one of the following cities was the first to attain the status of a ‘megacity?

A megacity is defined by the United Nations as an urban agglomeration with a total population exceeding 10 million people [2]. Historically, New York City was the first city in the world to reach this 10-million threshold, achieving the status in the 1950s [3]. While London was the first 'millionaire city' (reaching one million inhabitants by 1810) and the first to be described as a 'conurbation' [1], it did not reach megacity status until much later. By 1950, only New York and Tokyo were recognized as megacities. Other cities like Paris and Washington D.C. reached significant population milestones later or remain below the 10-million threshold for the city proper. Therefore, New York is widely credited as the world's first megacity [3].

Sources

1. [2] https://www.sciencedirect.com/topics/social-sciences/megacity
2. [3] https://education.nationalgeographic.org/resource/history-cities/
3. [1] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 14: Settlements > Conurbation and Metropolitan Regions > p. 37