The city of London became the largest city in the world by the late nineteenth century. It was the most powerful imperial centre by the beginning of the twentieth century. Various factors were responsible for it, as given below : Causes : (i) Increase in population. One out of every nine people of England and Wales lived in London. Industrial revolution started in Britain. The enclosures of farms and abolishment of corn laws made many farmers migrate to towns and cities such as London, Manchester and Leeds. Migrants from rural areas were attracted to the textile mills of Manchester and Leeds in large numbers after the 1850s. (ii) Colonisation and political dominance in global trade led to great wealth and capital,making London the hub of world trade and commerce. (iii) The population expanded throughout the nineteenth century from one million in 1810 to 4 million in 1880. They constituted aristocrats, administrators, semi-skilled and skilled artisans, workers, traders, beggars, etc. (iv) Important industries were the dockyards, clothing, footwear, metallurgy, etc. (v) During the First World War, London began manufacturing motor cars and electrical goods.