The English Channel is a body of water that separates England from France and joins the North Sea and the Atlantic Ocean. The channel is 350 miles long, and it has been a significant part of human history; any invasion of England from France or vice versa would have to take place across the channel, leading to the channel being the site of several naval battles during the various wars between the two countries, notably during the Napoleonic Wars. Napoleon I's ambitions to conquer Britain were thwarted by British naval superiority in the Channel, and Adolf Hitler was also forced to deal with the fact that Britain was an island, and therefore could only be attacked by sea or by air. The channel is one of Britain's greatest natural defenses, but Britain's physical separation from the European mainland had led to significant support for isolationism and Euroscepticism in British politics.