After the war, northern parts of Appalachia experienced an economic boom, while economies in the southern parts of the region stagnated, especially as Southern Democrats regained control of their respective state legislatures at the end of Reconstruction. Pittsburgh as well as Knoxville grew into major industrial centers, especially regarding iron and steel production. By 1900, the Chattanooga area and north Georgia and northern Alabama had experienced similar changes due to manufacturing booms in Atlanta and Birmingham at the edge of the Appalachian region. Railroad construction between the 1880s and early 20th century gave the greater nation access to the vast coalfields in central Appalachia, making the economy in that part of the region practically synonymous with coal mining. As the nationwide demand for lumber skyrocketed, lumber firms turned to the virgin forests of southern Appalachia, using sawmill and logging railroad innovations to reach remote timber stands. The Tri-Cities area of Tennessee and Virginia and the Kanawha Valley of West Virginia became major petrochemical production centers.