In 1885 the work of the "Association" was recognized by the Congress of Berlin, the sovereign of Belgium becoming the sovereign of the Congo Free State. The treaty of Berlin stipulated that trade should remain free in the new State, that the natives should be protected and that slavery should be suppressed. Four years later, the king, in his will, left the Congo to Belgium, "desiring to ensure to his beloved country the fruit of a work pursued during long years with the generous and devoted collaboration of many Belgians, and confident of thus securing for Belgium, if she was willing to use it, an indispensable outlet for her trade and industry and a new field for her children's activity." The work was pushed with indomitable energy. In 1894 a vigorous campaign against the Arab slave-traders was brought to a successful conclusion. In 1898 the first railway connecting Matadi, on the Lower Congo, with Leopoldville, on the Stanley Pool, opened the great waterway as far as the Stanley Falls. A flotilla was launched on the upper stream and its main affluents, while roads and telegraph lines spread all over the country. The financial situation, however, remained critical. The enterprise had absorbed the greater part of the king's personal fortune. The credits voted by the Belgian Chambers were inadequate, and, though a few financiers began by now to realize the enormous value of the enterprise, their number was not sufficient to ensure the immediate future. Faced with considerable difficulties, which compelled him to severely curtail his personal expenses, Leopold II had formally offered the colony to the country in 1895. This offer had been rejected. Under the stress of circumstances, the sovereign of the Congo Free State decided to exploit directly the natural resources of the land, mainly rubber and ivory. The natives were compelled to pay a tax in kind and vast concessions were granted to commercial companies whose actions could not be properly controlled. This semi-commercial, semi-political system was bound to lead to abuses, even a few State agents betraying the confidence which their chief had placed in them and oppressing the natives in order to exact a heavier tax.