From the second half of the eighteenth century Scotland was transformed by the process of Industrial Revolution, emerging as one of the commercial and industrial centres of the British Empire. It began with trade with Colonial America, first in tobacco and then rum, sugar and cotton. The cotton industry declined due to blockades during the American Civil War, but by this time Scotland had developed as a centre for coal mining, engineering, shipbuilding and the production of locomotives, with steel production largely replacing iron production in the late nineteenth century. This resulted in rapid urbanisation in the industrial belt that ran across the country from southwest to northeast; by 1900 the four industrialised counties of Lanarkshire, Renfrewshire, Dunbartonshire, and Ayrshire contained 44 per cent of the population. These industrial developments, while they brought work and wealth, were so rapid that housing, town-planning, and provision for public health did not keep pace with them, and for a time living conditions in some of the towns and cities were notoriously bad, with overcrowding, high infant mortality, and growing rates of tuberculosis. The new companies attracted rural workers, as well as large numbers immigrants from Catholic Ireland, changing the religious balance and national character, particularly in the urban centres of the west. In cities like Glasgow a sense of civic pride emerged as it expanded to become the "second city of the Empire", while the corporation remodelled the town and controlled transport, communications and housing.