England's only serious setback during the period 1660 to 1815 was the loss of the 13 colonies in America. As everyone knows, the overt cause of the war was George III's insistence on his right to tax American trade. But the real issue was deeper: the colonies had become a nation, and no nation can consent to be governed from without. Hardly a man in England understood that the crux of the matter was a new sense of nationality, and certainly the colonists did not, for they were "hot for their rights as Englishmen."
From the viewpoint of British sea power, the war was indeed stupid. At the time the colonies had over 2 million people as opposed to about 7.5 million in the British Isles. Given that population, the extent of their territory, coupled with the distance from England, there was little hope of holding them by force if any powerful nations were willing to help. Spain, smarting under the loss of Jamaica and Gibraltar, and France, smarting under the war of 1756 to 1763 and the loss of Canada, were certain to strike their ancient enemy sooner or later. England had won the Seven Years' War without the aid of an important Continental ally, but she had done so with the help of her colonies, and between 25 and 30 percent of the ships under the British flag were owned in her North American colonies. Without detracting from Bunker Hill, Valley Forge, and Yorktown, it is evident that Spanish and French sea power helped to decide American freedom. Three times after 1779, their combined fleets sailed into the English Channel, once in the force of 66 ships-of-theline, to send the British fleet scurrying to cover of home ports like rabbits. The French fleet, revived from its low ebb of 1756 to 1763, was at a high peak of efficiency, and a large force came to America under command of the Comte de Grasse. The 13 colonies gained their freedom, so Mahan points out, because the British fleet was not equal to the task placed upon it.