The agreement held and worked in spite of the opposition of groups of operators, notably in the West Virginia field and the steel district of Pittsburgh, and the individualistic lethargy of many of the miners. The new philosophy of business trade unionism gripped the miners, made the trade union policy triumphant over the vaguely utopian policy of the Knights of Labor, and resulted in the consolidation of the miners' organizations into the United Mine Workers of America in 1890. But the process of overdevelopment continued in the industry. The workings of the joint machinery creaked and faltered under the impact of strikes and lockouts due in the main to market fluctuations, and for a decade the United Mine Workers, in spite of periods of prosperity and rapid growth, was perpetually threatened with the fate of its predecessors. This fate was averted by the economic developments which had converted the compact anthracite field into a virtual monopoly under the combined control of the anthracite railroads and the great banking houses of the East that owned the railroads. While the bituminous industry sprawled and overdeveloped, the anthracite combination gradually restricted the production of anthracite to the calculable demand of the market. This made for stability in the anthracite field, which is reflected in the fact that while even today the average working year in the bituminous fields is approximately two hundred and fifteen days,--an average working day when spread over the year, of less than four hours,--the working year in the anthracite field gradually rose until today it holds steady at something more than two hundred and sixty days a year.