In the past, the vast majority of the world’s population lived in rural areas or small communities. Most people worked in agriculture or in areas related to agriculture. But, in the 19th century, this began to change in areas like Europe and the United States, where the Industrial Revolution spread to other countries, the move from country to city became a world-wide tendency. People believed, and still believe, that there are more opportunities in big cities than in rural areas. In fact, nowadays most of the world’s population live in urban areas. There are, of course, problems associated with rapid urbanization because many countries don’t have enough money to provide the infrastructure necessary to support an enormous population in their cities. There are not enough public facilities like hospitals, schools and roads. Traffic is a huge problem, and vehicles cause pollution. Sometimes there isn’t enough water for the needs of the population. Often the police are not prepared to combat the large amount of crime in a big city. For that reason, if urbanization continues the way it is now, there will be more and more problems in the world’s megacities.