The main problem he confronted was that neither he nor anyone in the German military had expected to face a war against a Britain determined to resist. Hitler had never had any intention of attacking Britain nor any part of her empire, it simply was not part of his plan for conquest in the East. Although he had expected Britain to object to his aggresion and, perhaps, even to declare war, Hitler had believed that Britain’s essential interests were not threatened by his actions. He had reasoned, therefore, that Britain would make peace once his conquests were an established fact.
It was the first real strategic failure that Hitler made in his military career. He had expected Britain to make peace. When she did not he had no pre-planned brilliant operation ready to knock her out of the war. The second, and much greater, strategic mistake was to follow the next year. With Britain still unsubdued, Hitler expanded the war by invading Russia. He had said before the conflict started that he would first have to ensure peace in the West before attacking East. He did not do so. Arguably this cost him his victory.
from "Hitler - Military Commander" by Rupert Matthews
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