Answer:
The world's urban population in the 1930s was about 20%, and by the 1970s, it had grown to about 35%.
Step-by-step explanation:
This phenomenon is known as urbanization, and consists in the increasing of the proportion of people who live in cities vs the proportion of the people who live in the countryside.
This is relevant because throughout history, the vast majority of people lived in the countryside as farmers, but when the industrial revolution started in the late 18th century, industry, and later services, began to slowly replace agriculture as the main economic activity of the world, and people began to move to cities to work in industry first, and later on, in the services.