Both Napoleon and Hitler controlled continental Europe. Neither could defeat Britain so long as she retained her mastery at sea, and for that reason both abandoned their projected invasion of the British Isles. But Britain could not hope to overcome her enemy without the help of major land-powers on the Continent. Spain in the 1800s was the equivalent to North Africa in the early 1940s, sideshows where alone the enemies grappled on land. Both dictators turned to a strategy of economic stranglehold of Britain, in the 1800s by attempting to close all European ports to British, in the 1940s by unlimited submarine warfare. In both wars the dictators invaded Russia to render her powerless so that they could turn all their strength against Britain, and both campaigns had the opposite result, that Russia became a victorious ally who enabled Britain to survive. The analogy breaks only in the attitude of the United States, in the first war a temporary enemy, in the second an incomparable ally.