Germany did not invade Sweden because Sweden was Germany's largest supplier of Iron Ore, without which the German economy would have collapsed.\n\nThis was the reason in 1940, before the invasion of France, Germany invaded Norway days ahead of a British-French invasion fleet at Narvik. During the winter time, the northern Swedish ports in the Baltic would freeze closed. Because the Germans had initially seized all of the major air fields in Norway, the Allied forces found themselves isolated and had to evacuate.\n\nAs an added bonus, the Germans were then able to use the Norwegian fjords both to launch submarines against Allied convoys supplying Soviet Russia and to sneak their warships such as the Bismark around the British blockade.\n\nThe previous answer is thinking of Switzerland, which did act as both a bank and a supplier of precision parts to Germany.