Naval warfare is no essential part of the armed conflict between contending States. In some cases it exercises a decisive influence on the conduct and issue of the conflict, in others none at all or next to none. But sea power, that is, the advantage which a nation at war derives from its superiority at sea, may largely affect the issue of a war, even though no naval engagements of any moment may take place. In the Crimean War the unchallenged supremacy of England and France on the seas alone made it possible for the Allies to invade the Crimea and undertake the siege of Sebastopol; while the naval campaigns of the Allies in the Baltic, although they resulted in no decisive naval operation, yet largely contributed to the success of the Allied arms in the Crimea by compelling Russia to keep in the north large bodies of troops which might otherwise have turned the scale against the Allies in the South. In the War of 1859, between France and Austria, with the Sardinian kingdom allied to the former, the superiority of the Allies at sea enabled considerable portions of the French army to be transported from French to Piedmontese ports, and by threatening the flank of the Austrian line of advance, it accelerated the concentration of the Allies on the Ticino. It also enabled the Allies to maintain a close blockade of the Austrian ports in the Adriatic, and might have led to an attack from the sea on the Austrian rear in Venetia had not the military reverses of Austria in Lombardy brought the war to an end. In the War of Secession in America the issue was largely determined, or at least accelerated, by the close but not impenetrable blockade established by the North over the ports and coasts of the South, and by the co-operation of Farragut on the Mississippi with the Federal land forces in that region. On the other hand, in the War of 1866 there was no naval conflict worth mentioning between Austria and Prussia, because Prussia had no navy to speak of; but as Italy, a naval Power, was the ally of Prussia, and as Austria had a small but very efficient naval force led by a great naval commander, the conflict between these two Powers led to the Battle of Lissa, in which the Italian fleet was decisively defeated, though the triumph of Prussia over the armies of Austria saved Italy from the worst consequences of defeat, and indeed obtained for her, in spite of her military reverses on land, the coveted possession of Venetia. In the War of 1870 again, although the supremacy of France on the seas was never seriously challenged by Prussia, yet her collapse on land was so sudden and complete that her superiority at sea availed her little or nothing. The maritime trade of Prussia was annihilated for the time, but it was then too insignificant a factor in the economic fabric of Prussia for its destruction to count for much, and the fleets of France rode triumphant in the North Sea and the Baltic; but finding