One of the circumstances which has played a part in determining the area of standardization in any industry is that success in the enforcement of collective agreements has depended largely upon whether all or most of the enterprises in competition with each other have been included in the same agreement. This circumstance has been sometimes decisive of the degree of centralized authority in the various trade unions. It has also tended to govern the attitude of particular trade unions towards the application of the principle of standardization without variation or modification.[103] The history of trade unionism is full of instances of organizations which have striven in vain to maintain uniform standardized wage rates throughout imperfectly organized areas.[104] Even when wage disputes have been settled by public agency, the usual procedure in the past has been to make the area covered by the agreement entirely dependent upon the area of dispute.[105] For all of that there has been in recent years a steady drift towards an extension of the area of standardization. In various industries careful thought has been given to the possibility of standardization on a national scale, though at present very few unions enforce such a scale.[106] On the railroads there are at present nation-wide wage scales. In Great Britain, to-day this is one of the most vexed of questions. Indeed Great Britain just has gone through a great coal strike in which it was one of the two great issues. The miners asked that "a levy be made upon each colliery company on every ton of coal raised to the surface to be used for ensuring the payment of wages agreed upon in a national wages settlement." The miners argue, and correctly, that district settlements would give unequal reward to men doing precisely the same work, and called upon for the same service.[107] 8.--The introduction of standardization into crafts or industries in which a variety of wage rates for substantially the same tasks exist gives rise to one other difficult problem. That is the determination of the level of standardization for each occupation.