In the late 19th century, the post-Civil War Industrial Revolution and the expansion of the nation's railroads brought a soaring demand for coal, and mining operations expanded rapidly across Appalachia. Hundreds of thousands of workers poured into the region from across the United States and from overseas, essentially overhauling the cultural makeup of eastern Kentucky, West Virginia, and western Pennsylvania. Mining corporations gained considerable influence in state and municipal governments, especially as they often owned the entire towns in which the miners lived. The mining industry was vulnerable to economic downturns, however, and booms and busts were frequent, with major booms occurring during World War I and II, and the worst bust occurring during the Great Depression. The Appalachian mining industry also saw some of the nation's bloodiest labor strife between the 1890s and the 1930s. Mining-related injuries and deaths were not uncommon, and ailments such as black lung disease afflicted miners throughout the 20th century. After World War II, innovations in mechanization (such as longwall mining) and competition from oil and natural gas led to a decline in the region's mining operations. Environmental restrictions, such as those placed on high-sulfur coal in the 1980s, brought further mine closures. While with annual earnings of $55,000, Appalachian miners make more than most other local workers, Appalachian coal mining employed just under 50,000 in 2004.