The last century has shown us quite clearly that migration into cities is the trend of the present and the future. In 1800, it is estimated that less than 3% of the world's population called cities their home. By the turn of the 21st century, this number had exploded, with some experts estimating that nearly half of all people lived in cities. This massive migration out of the country and into the city has lead to the rise of the megacity, a term typically used to describe a city with a population of over 10,000,000 inhabitants.
Cities have been a part of human civilization for thousands of years, rising from early tribes as symbols of power, commerce, and gathering places for cultural and religious events. As society has moved away from agricultural pursuits that require large amounts of land, the development and growth of cities has naturally increased dramatically. Although there are many factors that have led to the development of megacities, dependence on technology, population growth, and the economic development of poor nations are often described as major contributors to their rise.
It is somewhat difficult to get an accurate count of city dwellers, as population censuses are somewhat inaccurate in their estimation. Additionally, some dispute arises among experts as to what outlying city areas, such as suburbs, are meant to be included in the population count. Regardless of these difficulties, it is widely believed that at least 26 cities meet the criteria of 10 million inhabitants, with many additional cities on the cusp of joining. Tokyo, with more than 35 million residents, is currently the largest megacity.
Megacities allow convenience and good opportunities to find work, but they are fraught with complicated problems. Many of the traditional cities, such as New York City and Los Angeles, were not built to hold so many citizens, and are faced with countless issues of how and where to expand to accommodate their increasing populations. Sanitation, crime, and poverty are severe issues a megacity must face, and few have found sufficient ways to deal with these problems. But possibly the greatest challenge a megacity will face is the development of slums or shanty-towns along the border of the developed city.
The modern megacity is hardly restricted to wealthy countries such as the United States; in fact they are more common in countries where there is a tremendous economic division between the rich and the poor. Consequently, people who desperately need work only available in the city cannot afford to live there, and are forced to live in unsafe, inexpensive slums. Slum areas are typically hotbeds of crime and severe sanitation problems, leading to extremely high mortality rates and the danger of fast-spreading diseases. Since many slums are also built illegally, they leave residents in severe danger in the wake of natural disasters such as earthquakes or floods.
The megacity, according to most population experts, is here to stay despite its problems. Optimists hope that the development of a global community will help dispel some of the problems inherent to a megacity by promoting the economy of developing nations. Yet the megacity has long been a favorite setting of bleak works of fiction that depict a tightly-controlled, environmentally devastating future for city inhabitants. By the middle of the 21st century, it is believed that three out of five people will be living in cities; clearly the time for finding solutions to the problems of a megacity is now.