Canada had declared war on Nazi Germany shortly after the Second World War began in early September 1939 but the United States remained neutral. By mid-1940, the situation in Europe had grown dire; Germany's military successes had led to the occupation of most of Europe, and most importantly, France, which surrendered in June 1940. With Germany in control or allied with nearly all of continental Europe, it began to develop plans for an invasion of the British Isles. Germany's seemingly unstoppable military, its submarine campaign against British merchant shipping, and its neutrality pact with the Soviet Union, convinced many, including American President Franklin Roosevelt, that Britain itself would soon be invaded or forced to surrender.