"By the early twentieth century, explosions caused by gas and dust accumulations in underground coal mines boomed across the mountains of West Virginia, causing hundreds of deaths. An explosion that shot through the connected Monongah No. 6 and No. 8 mines near Fairmont in 1907 left more than 360 miners dead and rbought about the nation's first federal mine safety regulations. The Monongah blast remains the biggest mine disaster in United States history. Coal miners seeking better pay and safer working conditions through unionization clashed frequently with coal operators during the early 1900s. While union miners relied mainly on work stoppages and intimidation of strikebreakers to boost their cause, coal operators turned to strong-arm detective agencies, hired guns, machine gun-equipped locomotives, and even bomb-dropping aircraft to enforce their will. Coalfield hostilities reached the boiling point in August of 1921, when thousands of well-armed miners marched from Kanawha County to Blair Mountain on the Boone-Logan County line, where an army of mercenaries hired by coal operators awaited them in trenches fortified with machine gun nests. The ensuing Battle of Blair Mountain is considered the largest civil insurrection since the Civil War."