The first cities appeared thousands of years ago. They were built in places where the land was good for farming. As hunters and gatherers, people used to move from place to place. As farmers, they settled down, and as farming grew, so did cities.

For the next several thousands of years, cities kept growing. Some ancient cities have shrunk or disappeared, but many grew into even larger modern cities.

People Left Rural Areas for Big Cities

Today, living in a big city has become very common. This was not the case until quite recently. Most people used to live in the countryside. In 1800, less than 10 percent of the world's population lived in cities. In the United States, it was less than 6 percent. By 1900, however, about 40 percent of Americans were living in cities.

One of the main causes was the Industrial Revolution. During the Industrial Revolution, factories started being built in cities. This created a demand for workers in cities. Millions of people moved from the countryside to become factory workers.

Soon, cities became enormous. In 1800, London, England, had a population of about one million. Ten years later, it was home to about six million. By 1950, New York City, New York, U.S., became the largest city in the world, with a population of 12.5 million.

Thanks to new technologies, cities could grow upward, not just outward. Steel, a new and strong kind of metal, was invented. Steel gave birth to skyscrapers, buildings with 40 floors or more. Elevators were invented around the same time, which made skyscrapers usable.

The Rise of the Megacity

Today, over half the world's population lives in cities. By 2050, it will be about two-thirds. Much of this growth will come from families in cities having more children. It will also be driven by the movement of people from the countryside to cities.

All this growth has led to the rise of megacities, cities with a population of 10 million or more. New York City and Tokyo, Japan, became the world's first megacities in the 1950s. By 2018, there were 37 megacities across the planet.

Today, cities in Asia and Africa are growing the fastest. In 2019, Tokyo was the world's largest city. It has more than 37 million people. Delhi, in India, has almost 30 million. Shanghai, China; Mexico City, Mexico; and São Paulo, Brazil, all have populations well over 20 million.

Some Cities Struggle to Provide Services

Experts think that there will be 41 megacities by the year 2030. India already has five cities with over 10 million people. By 2030, it is expected to have seven. Kinshasa, the capital of the Democratic Republic of the Congo, has a population of 11.6 million. It is growing so quickly that it may soon become one of the largest cities in the world.

Many cities in Asia and Africa are struggling to provide services to their quickly growing populations. The same problem was common in Europe and North America during the Industrial Revolution. Lagos, Nigeria, the largest city in Africa, has 12.6 million residents. About two-thirds of them live in overcrowded slums. These poor neighborhoods often have dangerous living conditions. Slums often appear when cities grow quickly.

Nevertheless, megacities continue to expand. They will keep growing for years to come.