Hitler worked an apparent economic miracle by building autobahns, wireless sets and secretly re-arming, illegally building up shipping, u boats, tanks etc. All stuff he would need to mobilise his forces and disseminate his propaganda when he got the chance. He paid for all this by theft and eventually plundering the gold reserves of the European nations he invaded. And nobody stopped him when they were able. Maybe you should find out about the League of Nations and the policy of appeasement.
Hitler never attained air superiority in the west which hampered his invasion plans of Britain, he made the mistake of attacking the USSR in the erroneous belief that Stalin's purges had left the Red Army weakened, and declared war on the USA, trounced into it by the Japanese, before concluding Barbarossa. He had huge numbers of troops tied up in occupied Europe, the Reich becoming less tenable, the larger it grew.