Yet this State has not so far been a success. American immigration on any large scale ceased with the outbreak of the American Civil War and the emancipation of American slaves. The natives of the Kru coast and of the Muhammadan interior spurned any idea of being governed or taxed by foreign Europeanized negroes; and the Americo-Liberians lacked either the courage or the monetary means to effect a conquest of the regions outside the portions of the coast belt on which they had built their towns and established their plantations. As the more vigorous among the American negroes and mulattoes, who had started the settlement, died out, the younger generation failed to bring a similar degree of energy into the development of their native country. All had their faces far too much turned towards either America or England. English, of course, was and remained the official language of Liberia, its adoption being facilitated by the close connection between the Kru population and British West Coast trade (many Krumen also served, and serve still, in the British Navy); the constitution of the Republic was closely, too closely, modelled on that of the United States; very little interest was taken in the languages, history, manners and customs of the million and a half of Liberian aborigines, or in the wonderful native flora and fauna[107]. With the exception of the journeys of Benjamin Anderson in the sixties of the last century, there arose no Liberian explorer of any note who revealed anything about the geography or natural history of the hinterland. This indeed remained (geographically) a closed book down to 1903, when a series of explorations by British, French, Swiss, German and Dutch explorers at last brought to light by 1910 the main features of Liberian geography and ethnology. British and German traders and pioneers (not Americo-Liberians) alone discovered and worked the gold and diamonds of western Liberia and the rubber forests of the centre and east.