Aside from those already cited see: ROBERT FULTON, ENGINEER AND ARTIST, H. W. Dickinson, 1913. THE STORY OF THE GUNS, J. E. Tennant, 1864. THE BRITISH NAVY, Sir Thomas Brassey, 1884. CLOWES' HISTORY OF THE ROYAL NAVY, Vol. VII (p. 20, bibliography). NAVAL DEVELOPMENT OF THE 19TH CENTURY, N. Barnaby, 1904. THE TORPEDO IN PEACE AND WAR, F. T. Jane, 1898. SUBMARINE WARFARE, H. C. Fyfe, 1902. THE SUBMARINE IN WAR AND PEACE, Simon Lake, 1918. FOUR MODERN NAVAL CAMPAIGNS, Lissa, W. L. Clowes, 1902. THE AUSTRO-ITALIAN NAVAL WAR, Journal of the United Service Institution, Vol. XI, pp. 104ff. CHAPTER XV RIVALRY FOR WORLD POWER Even more significant in its relation to sea power than the revolution in armaments during the 19th century was the extraordinary growth of ocean commerce. The total value of the world's import and export trade in 1800 amounted in round numbers to 1-1/2 billion dollars, in 1850 to 4 billion, and in 1900 to nearly 24 billion. In other words, during a period in which the population of the world was not more than tripled, its international exchange of commodities was increased 16-fold. This growth was of course made possible largely by progress in manufacturing, increased use of steam navigation, and vastly greater output of coal and iron.[1] At the end of the Napoleonic wars England was the only great commercial and industrial state. At the close of the century, though with her colonies she still controlled one-fourth of the world's foreign trade, she faced aggressive rivals in the field. The United States after her Civil War, and Germany after her unification and the Franco-Prussian War, had achieved an immense industrial development, opening up resources in coal and iron that made them formidable competitors. Germany in particular, a late comer in the colonial field, felt that her future lay upon the seas, as a means of securing access on favorable terms to world markets and raw materials. Other nations also realized that their continued growth and prosperity would depend upon commercial expansion. This might be accomplished in a measure by cheaper production and superior business organization, but could be greatly aided by political means--by colonial activity, by securing control or special privileges in unexploited areas and backward states, by building up a merchant fleet under the national flag. Obviously, since the seas join the continents and form the great highways of trade, this commercial and political expansion would give increased importance to naval power. [Footnote 1: Coal production increased during the century from 11.6 million tons to 610 million, and pig iron from half a million tons to 37 million. Figures from Day, HISTORY OF COMMERCE, Ch. XXVIII.]