In the 19th century, the Industrial Revolution led to a dramatic increase in factory production in the United States. The demand for workers increased, and many new positions were filled by children. By 1900, about twenty percent of all children in the United States were employed, and some of those working in factories were only four years old. The work was difficult and dangerous, leaving many child laborers with health problems. Factory owners turned to child labor for several reasons. For example, children could be paid less than adult workers. They were also less likely to go on strike.