Geopolitical constants have ensured that Britain, an island off a continental land mass, used similar defence strategies when faced with an overmighty power dominating Europe. In the last five hundred years the same general pattern can be discerned – when Elizabeth I and Lord Burleigh were faced with the Spanish power of Philip II in the sixteenth century, when William III formed his Grand Alliance against Louis XIV in the seventeenth century, when Britain was facing the armies of Revolutionary and Napoleonic France; and if you add the further dimension of air power, when in the twentieth century the danger of Hitler's Germany was from the ports of north-west France. British defence generally took three forms. The navy would send an expedition or mount a blockade of continental ports controlled by the enemy. Secondly, flotillas of small warships would take up defensive positions around the south and east coasts, not only as defence against invasion but as protection for coastal trade. Thirdly, ports and vulnerable beaches would be fortified and manned by the army, supported by militia, to ensure that at the least an invading force would be compelled to make a large-scale military effort, making a surprise attack by a small mobile force unviable. In conjunction with these naval and military measures, Britain would traditionally sign treaties and lesser agreements with other European powers alarmed at the growth of the one great power, and these treaties were often bolstered by subsidies.

It was not possible for Britain just to withdraw behind Channel fortifications and leave the powers of Europe to fight it out, as has recently been argued in discussions about the First World War. At the end of the eighteenth century ties between Britain and the Continent were even more complicated than they were in the twentieth century. Here there is space only to point to the Austrian Netherlands, as these territories were in 1792, from which a hostile power could launch an invasion, dangerously near the Thames Estuary and the Essex rivers. In addition, Hanover was still tied to the British crown, with no natural frontiers and indefensible, ‘a tempting bait permanently dangled before the open jaws of the French army’. In addition, an absolute necessity lay in maintaining trade with north-west Europe, not only because it was by far the largest market for British exports.