Until recent years, the vast majority of people lived in the countryside. In 1800, for instance, less than 10% of the world's population were city-dwellers. In the United States, less than 6% of people lived in cities. By 1900, however, this number had increased to about 40%, and today, more than half the world’s population resides in urban areas.

People move to cities for many reasons. Some are attracted (or pulled) to the city for work. Some are forced (or pushed) from the countryside because of problems there. People might lose their farms because of drought, flooding or other environmental factors. Sickness and war or violence can also force people off their land. Many of these people may seek new opportunities in a city.

The first cities appeared thousands of years ago. Around 7500 B.C.E., communities began to arise in places where the land was good for farming, such as Mesopotamia (modern-day Iraq). Cities also formed along the Nile River in Egypt and Sudan, the Indus River Valley on the Indian subcontinent and the Huang He (or Yellow River) in China. These were the first farmers. Prior to this, all people moved from place to place, following herds of animals or gathering food from the forests. When people began to plant food, they stayed in one place—on fertile land. Nearby waterways provided a much-needed transportation system, making it possible for early farmers and city-dwellers to engage in trade.

For the next several thousands of years, cities continued to grow in number, size and importance. Japan’s capital, Tokyo, was established during the Tokugawa period, which began in 1603. It grew as a center of military and government power. Today, Tokyo is still one of the world’s largest and most important cities.

Other cities that were once among the largest in the world, such as the cities of Mesopotamia, no longer exist, while others remain but are much smaller than in the past. A city’s population can decline for many reasons, including an invasion from other states or countries, or a war within one’s country. A city may also lose its population due to economic downturns, food shortages, disasters or environmental problems.

Some cities go through cycles of growth and decline. Istanbul in Türkiye is one such city. It was once the capital of two empires, the Eastern Roman Empire and the Ottoman Empire. But there were also periods of decreasing population because of disease and war.

Migration from Rural to Urban Areas

Some periods in history have witnessed faster periods of urbanization—or growth of cities—than others. Take, for example, the Industrial Revolution. The Industrial Revolution began in England toward the middle of the 18th century and spread to the United States and other parts of Europe. The Industrial Revolution introduced new machines to do the work that was once done by hand. As a result, thousands of factories were built in cities, creating a demand for workers. Over the next century, millions of people in the United States and Europe moved from farms to cities. London, U.K., grew from a population of 1 million in 1800 to over 6 million a decade later. Growth continued for the next two centuries. By 1950, New York City, U.S., became the largest city in the world, with a population of 12.5 million.

As the Industrial Revolution spread to other parts of the world, cities grew there as well. In many Asian, African and South American countries, colonizers exploited raw materials and labor to fuel the industrial growth of the colonizing nation. When countries became independent, they continued to look for economic growth through industrialization, which fueled the growth of cities.

The Rise of the Megacity

All of this growth has led to a new type of city: the megacity, which is defined as having a population of 10 million or more. New York City and Tokyo became the world's first megacities in the 1950s. By 2023, there were 34 megacities across the globe. As of 2023, Tokyo, with more than 37 million residents, is the world's largest city. Delhi, in India, has a population of more than 30 million. Shanghai, China, Mexico City, Mexico, and São Paulo, Brazil, all have populations well over 20 million.

Challenges That Cities Face

Around the world, the fastest-growing cities face many challenges. Many struggle to build infrastructure—such as transportation networks, hospitals, schools and utilities—to keep up with growing populations. Problems with infrastructure can lead to problems in other areas. For example, people can get sick if they do not have proper sanitation and plumbing.

Many cities are implementing innovative plans to make infrastructure better. For example, Barranquilla, Colombia, developed a plan that included building urban parks. The goal was to have everyone live within walking distance of a public park. The effects went beyond just having green space for people; the parks also increased community pride and reduced crime.

Another challenge for cities is providing health services. Cities can often get residents to help with health services in unique ways. In Maputo, Mozambique, the government asked community leaders to write reports about neighborhood toilet facilities. Most people in neighborhoods had latrines (simple toilets created by digging holes in the ground). The government was still gathering information when community members set about fixing the problem. Residents began to fix their latrines themselves, which improved sanitation and health outcomes.

Challenges to cities also come from climate change. City residents experiencing poverty have a harder time recovering from natural disasters like floods and wildfires. But cities can also combat climate change. Lima, Peru, is located in a desert with little rain but heavy fog. Scientists in the city have created a way to strip water from fog. This is less expensive than transporting water in other ways, and it saves energy.

Addressing poverty is also a challenge that city governments must face. People are sometimes pushed toward cities when they experience job loss. People can also be driven out of rural areas because of violence. They might even lose a job in agriculture due to widespread droughts or other natural disasters. If migrants have trouble finding work, they may fall even deeper into poverty. Cites are trying new ways to address poverty. Cities in Finland, for example, use a program called Housing First. In this program, people are given free housing. Then they can get other support through job training programs or drug counseling. This is different from other countries where people must get training or drug counseling before receiving housing. This program has helped decrease homelessness in Finland.

City populations are expected to grow in the future. The urban population is predicted to increase to around two-thirds of the global population by 2050. The United Nations predicts that there will be 41 megacities by 2030. Government leaders and citizens must work together to prepare for and face issues that bigger cities bring.