The causes of the war of 1812-15 must be sought in the history of Europe and the relations between England and the United States for several decades before it actually broke out. Great Britain was engaged in a supreme struggle not only for national existence but even for the liberties of Europe, from the moment when Napoleon, in pursuance of his overweening ambition, led his armies over the continent on those victorious marches which only ended amid the ice and snow of Russia. Britain's battles were mainly to be fought on the sea where her great fleet made her supreme. The restriction of all commerce that was not British was a necessary element in the assertion of her naval superiority. If neutral nations were to be allowed freely to carry the produce of the colonies of Powers with whom Great Britain was at war, then they were practically acting as allies of her enemies, and were liable to search and seizure. For some time, however, Great Britain thought it expedient to concur in the practice that when a cargo was trans-shipped in the United States, and paid a duty there, it became to all intents and purposes American property and might be carried to a foreign country and there sold, as if it were the actual produce of the republic itself. This became a very profitable business to the merchants of the United States, as a neutral nation, during the years when Great Britain was at war with France, since they controlled a large proportion of all foreign commerce. Frauds constantly occurred during the continuance of this traffic, and at last British statesmen felt the injury to their commerce was so great that the practice was changed to one which made American vessels liable to be seized and condemned in British prize courts whenever it was clear that their cargoes were not American produce, but were actually purchased at the port of an enemy. Even provisions purchased from an enemy or its colonies were considered "contraband of war" on the ground that they afforded actual aid and encouragement to an enemy. The United States urged at first that only military stores could fall under this category, and eventually went so far as to assert the principle that under all circumstances "free ships make free goods," and that neutral ships had a right to carry any property, even that of a nation at war with another power, and to trade when and where they liked without fear of capture. England, however, would not admit in those days of trial principles which would practically make a neutral nation an ally of her foe. She persisted in restricting the commerce of the United States by all the force she had upon the sea.