Today, many people live in big cities, but this was not always the case. In 1800, more than 90% of the world's population lived in the countryside. In the United States, fewer than 6% of people lived in cities. By 1900, this number had increased to about 40%.

People move to cities for many reasons. Some are drawn by new job opportunities. Others are forced out of the countryside. People might lose their farms because of drought or floods. Sickness, war and violence can also force people out of the country and into cities.

The first cities appeared thousands of years ago, around 3,000 B.C.E. These cities grew in places where the land was good for farming. As hunters and gatherers, people used to move from place to place. When they began to farm, they stayed in one place to grow crops. The first cities, such as Ur in Mesopotamia, were built near water. The water could feed the plants. In addition, nearby waterways provided a transportation system, making it possible to trade with neighboring cities.

Since those early cities, they have continued to grow in number, size and importance. Tokyo, Japan, became an important city in the 1600s, partly because it was the center of Japan’s military power. Today, Tokyo is still one of the world’s largest and most important cities.

Some cities that were once among the largest in the world, like the cities of Mesopotamia (present-day Iraq), no longer exist. Others have shrunk in size. Cities often see a decline in population due to war, the outbreak of disease, or a lack of money and resources to support their population.

Some cities grow in population, then shrink, then grow again. An example is Istanbul in Türkiye. At some points in history, it was important. It was the capital of two different empires. But other times, its population decreased. In 1204, people fled when the city was invaded. Later, in the 17th century, a disease called the bubonic plague spread through the city, causing many deaths. People also fled the disease-ridden city to the countryside.

People Left Rural Areas for Big Cities

One of the main reasons for the growth of cities was the Industrial Revolution. This huge change introduced new machines that could do work that was once done by humans or other animals. It began in England toward the middle of the 1700s and spread to the United States and other parts of Europe. Then, it spread to Asia, Africa and South America.

The machines of the Industrial Revolution were housed in factories. Many of these factories were in cities. They needed workers. Over the next hundred years, people moved from farms to cities to work in the factories. London, England, had a population of 1 million in 1800. In 1810, its population had grown to over 6 million. New York City also grew. By 1950, it had a population of 12.5 million, making it the largest city in the world.

As factories were built in other parts of the world, cities grew there as well. European countries set up colonies in Asia, Africa and South America. They used the raw materials from these places to fuel their factories. Sometimes they set up factories in their colonies because they did not have to pay workers as much. The factory owners often abused the workers in those colonies. When these countries became independent, businesses set up their own factories. The growth of cities continued.

The Rise of the Megacity

All of this growth has led to a new kind of city, the megacity. A megacity is a city with a population greater than 10 million. New York City and Tokyo became the world's first megacities in the 1950s. By 2023, there were 34 megacities across the globe.

In 2023, Tokyo was the world's largest city. It has more than 37 million people. The population of Delhi, India, is more than 30 million. Megacities exist all over the world. Shanghai (China), Mexico City (Mexico) and São Paulo (Brazil) all have populations much higher than 20 million.

Challenges Cities Face

Cities face many challenges, especially when they grow quickly. Many of the fastest-growing cities are in the Middle East, Asia and Africa.

Often, cities cannot keep up with the needs of their growing populations. They cannot build roads fast enough. Residential areas, hospitals and schools become overcrowded. Many cities look for ways to solve these problems. Barranquilla, Colombia, for example, added new parks. Having a park nearby helped build pride. The city experienced less crime in neighborhoods where the parks were built.

Another challenge is stopping the spread of disease. When people live close together, disease can spread more quickly. In addition, some cities do not have enough resources to pick up waste and keep water clean. Cities look for solutions. Their people often can help. Some of the neighborhoods in Maputo, Mozambique, for example, had latrines, which are like toilets with holes in the ground. There were no sewers or pipes to take away the wastewater. After community leaders noted the problems, many people fixed the latrines. This made neighborhoods cleaner and healthier.

Climate change makes problems in cities worse. For example, it can cause droughts and flooding, which harm cities. These problems are harder for people living in poverty. City leaders look for ways to deal with climate change. Scientists in Lima, Peru, for example, have figured out a way to extract water from fog. Lima is in a desert and gets little rainfall. Having water from fog is an important solution.

Too many people in cities live in poverty. Many people come to cities in search of jobs. They have skills, but these skills might not match the available jobs. This can make poverty worse. Sometimes, cities work hard to help people in poverty. An organization in Finland, for example, makes sure that people have homes. Other countries provide people with job training.

City populations are expected to grow in the future. The United Nations predicts there will be 41 megacities by the year 2030. Leaders must be prepared for the challenges of managing large, rapidly growing cities.