Historians treating the American-Mexican diplomatic crisis during the Hayes administration have tended to regard it as a political and military affair, involving such points of controversy as the American recognition of Porfirio Díaz, the Mexican inability to keep order on the frontier, invasions of Mexico by American troops to punish marauding Indians, and, behind and above all, Mexican fears of American territorial ambitions. No one will deny that these dramatic circumstances deserve attention, but some writers have largely ignored the economic side of the question. Under cover of the rifle fire along the border and the excited buzzing in the government offices American business promoters, long anxious to take part in the development of Mexican resources, finally obtained the terms which would make this development possible. In September, 1880, after three years of controversy and war scares had almost extinguished American hopes, the Mexican government granted generous concessions for the building of the Mexican Central and the Mexican National Railroads and, in so doing, opened the way for an inrush of American capital.