Again, we really can't emphasize enough the degree of confusion in German foreign policy planning during this period. The critical issue for Germany was to get England out of the war. In order to do that, a creative policy needed to be introduced. It was also important to reduce support for England in the United States. No coherent plan was developed for either of these goals. In America, contrary to a lot of myths, yes, there was an isolationist - so-called isolationist - that was in a pejorative. There was an antiwar lobby to oppose getting America into a war in Europe. But a far greater lobby was the pro-war lobby, which was funded by big business interests, and they must've probably outspent the supposedly dangerous isolationists about 10 to 1.
On top of that, Roosevelt was strongly in favor of getting America into the war against Germany. So, we need to get away from little myths of tiny little England fighting big, big Germany. The overwhelming preponderance of forces was still against Germany. Germany's position was a lot weaker than it looked, and the the entire continent Europe became a subject of the Anglo-American blockade. Also, Germany did a very poor job, unlike the absorption of Bohemia and Moravia. Germany did a very poor job of absorbing and mobilizing the industrial resources for war in the territories that it occupied.
Anyway, the Germans were still subject to air attack from England. So again, the notion that the Germans woke up one day and wanted to be mean and attack England, that's not true. The English were bombing Germany. So, combined with the idea of trying to take over England, the Germans launched what was called the Battle of Britain, which, frankly, was a military stupidity from day one. The Germans did not have the capability to knock out the British Air Force. They certainly didn't have the capability to invade England. And even if they had invaded England, it wouldn't have accomplished all that much other than leading to a bloodbath, because the British fleet simply would've left, and Britain would've resumed the supervision of its empire from America.
So, this was an ill-conceived idea from day one that was very damaging to Germany. The Luftwaffe was severely damaged in the failed attempt to launch the Battle of Britain. Probably the greatest hope that Germany had militarily of ending the war was in the Mediterranean. There's been a lot of talk of what would've happened if Spain and entered the war. Well, obviously that probably wouldn't have been very good for England, but Germany could've shut England out of the Mediterranean without Spain. It didn't need Spain. If you look at the map, had sufficient air resources been stationed, and sea resources been stationed in Sicily and Italian Africa, you could've simply closed the Mediterranean right then and there. Had Britain lost Egypt and from Egypt, as Rommel planned, the German armies could've moved into places like Iraq, and the whole Arab world was highly supportive of Germany. There would've been an enormous pressure on England to get out of the war. But that was not done. Instead, the ill-conceived Battle of Britain was launched, which is basically a disaster for Germany.