The mining companies refused Agree_or_refuse_to_act to meet the demands Request of the workers and instead hired Employment Baldwin-Felts agents equipped Supply with high-powered rifles to guard Patrolling the mines and act as strikebreakers .

A month after the strike began Process_start , hostilities began Process_start with the arrival of the Baldwin-Felts Agents who provoked Causation the miners .

On May 19 , 1920 , a shootout Hostile_encounter in Matewan , West Virginia , between agents of the Baldwin-Felts and local miners , who later joined Becoming_a_member the United Mine Workers of America , sparked Process_start what became Becoming known as the Battle of Blair Mountain , the largest insurrection in the United States since the American Civil War .