The 19th century saw significant development in the sciences which led to advances later in the 20th century. Great Britain's Industrial Revolution spread to North America, Japan and continental Europe. Advances in medicine and a better understanding of human anatomy and disease prevention occurred. Because of this, populations in the western world grew rapidly. Europe's population doubled during this century and London became the world's largest city. Railroads were built and not only influenced the way people obtained goods but also aided in the creation of larger cities.