Around the same time, improvements in farming technology greatly increased food production. This made it possible for much larger groups of people to live closer together. But then fewer workers were needed on farms, making more of them available to go to work in factories.

These factories helped to spark the growth of cities. In 1801 in England and Wales, there were only 106 "cities" or places with 5,000 people or more. By 1891 there were 622, with larger numbers of the population. Similar changes were also taking place in the United States, as hundreds of thousands of immigrants arrived looking for jobs and a better life.

Humans have been interested in the moon, stars, and planets for thousands of years. In the 20th century, we finally developed technology to safely send astronauts into space to explore the moon and work on the International Space Station. Different kinds of technology are used to meet human needs when people travel beyond Earth’s atmosphere. Humans have several needs that must be met to survive in any extreme environment on Earth or in space. We need to have oxygen to breathe, water to drink, food to eat, a way to store or remove waste, a certain temperature to keep our body safe, some light (but protection from too much direct sunlight), and the correct pressure so our organs don’t collapse or explode. We use different kinds of technology to meet all of these needs in space.