As the mines were dug deeper, they became more dangerous, and the work more arduous, creating the conditions for conflict. In 1880, Colorado Governor Pitkin, a Republican, declared martial law to suppress a violent mining strike at Leadville. In the 1890s many Colorado miners began to form unions in order to protect themselves. The mine operators often formed mine owners' associations in response, setting up the conditions for a conflict. Notable labor disputes between hard rock miners and the mine operators included the Cripple Creek strike of 1894 and the Colorado Labor Wars of 1903–04.