Cambria Iron Company
The economic heart of Johnstown was the Cambria Iron Company, which opened in 1852 with the arrival of the Pennsylvania Railroad in Johnstown. In 1857, William Kelley developed a process at Cambria for purifying iron into steel in large quantities, dramatically increasing the usefulness and value of the mill's products. Within a few years, the Johnstown mills and other mills further upstream in the Conemaugh Valley were running continuously to meet the burgeoning demand throughout the country. By 1900, half of the nation's steel was made in Pennsylvania. Bethlehem Steel bought Cambria in 1923.
During World War II, southern and western states began building steel mills, making older plants in Pennsylvania increasingly obsolete and too expensive to upgrade. Diesel locomotives and trucks replaced coal-fueled steam locomotives for transporting the nations goods. This lead to a slow decline of the steel industry in Johnstown, culminating in the closing of the Johnstown mill in 1988 and bankruptcy for Bethlehem Steel. (reference)