After rioting by Baltimore and Ohio Railroad workers and the deaths of nine rail workers at the hands of the Maryland militia, workers in Pittsburgh, Pennsylvania, stage a sympathy strike that is met with an assault by the state militia.

The Baltimore and Ohio Railroad was the oldest railroad in the United States and the first steam-operated common carrier. Construction of the line began in 1828, and it operated as B&O from 1830 until 1987, when it was merged into the Chessie System. Its lines are today controlled by CSX Transportation.

The Great Railroad Strike of 1877, sometimes referred to as the Great Upheaval, began on July 14 in Martinsburg, West Virginia, after the Baltimore and Ohio Railroad (B&O) cut wages for the third time in a year. The Great Railroad Strike of 1877 was the first strike that spread across multiple states in the U.S. The strike ended 52 days later, after it was put down by unofficial militias, the National Guard, and federal troops. Because of economic problems and pressure on wages by the railroads, workers in numerous other states, from New York, Pennsylvania, Maryland, Illinois and Missouri, also went on strike. An estimated 100 people were killed in the unrest across the country. In Martinsburg, Pittsburgh, Philadelphia and other cities, workers burned down and destroyed both physical facilities and the rolling stock of the railroads—engines and railroad cars. Some locals feared that workers were rising in revolution, similar to the Paris Commune of 1871, while others joined their efforts against the railroads.

Maryland is a state in the Southern and Mid-Atlantic regions of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east, as well as with the Atlantic Ocean to its east, and the national capital and federal district of Washington, D.C. to the southwest. With a total area of 12,407 square miles (32,130 km²), Maryland is the ninth-smallest state by land area, and its population of 6,177,224 ranks it the 18th-most populous state and the fifth-most densely populated. Maryland's capital city is Annapolis, and the state's most populous city is Baltimore.