If US wont come to rescue , German would have taken over the British Empire ..
German's were Damn good when it comes to Military Tactics ... and innovations ... the biggest mistake they have done was to open the second front with the USSR ... if Hitler continue the Peace Agreement with Stalin , he would have Destroyed the Entire UK , and able to face US ...
Nah, while Germany could have defeat UK in a land war, taking the British home soil would be much more difficult for the same why the Mongolian horde took much of Asia, but run into problems with Japan. A powerful land army does not necessarily translate into a similarly powerful navy.
Without opening the USSR front, the Germans could conceivability wore down the British eventually, but it will take a long time and what will happen at the mean time?
When reading WWII history, a lot of people forgot for all USSR's might during the war and after the war, USSR only started industrializing in 1928 (start of the first five year plan). Between 1928 and operation Barbarossa in 1941, USSR only had 13 years to build an industry, catch up in technology and modernize its army. Since industrialization is an exponential process, if Germans took five more years to defeat the British before it actually attacks the USSR, it would have been utterly crushed by USSR.
Whether it was foresight or not, Hitler actually attacked USSR at the perfect opportunity. When Operation Barbarossa occurred, the French has been destroyed. The Spanish was neutral. The Italian was Germany's ally. The British had withdrawn back to the British Isle and the Americans were recovering from one of the worst economic crisis in its history. USSR was on the verge of industrial boom, but still needed time to prepare. Basically, there could not really been a more opportune time to attack. The operation did eventually fail, but that was because the Russians were made of pretty stern stuff rather than mistake on German part.