Answer:
The correct answer is Urbanization
Urbanization is the shift of population from the rural areas to the urban areas. Urbanization causes cities to grow and the countryside to shrink in population. These phenomenon began to take force in the nineteenth century in cities like London or New York, but it was in the twentieth century when in took full force.
Currently, urbanization is a strong phenomenon in the two most populated countries in the world: India and China. This is why these two countries have many cities of over 1million people.
