The reason is that a military defeat of Britain will bring about the disintegration of the British Empire. This would not be of any benefit to Germany.

Halder appeared on the 29 June 1942 cover of Time magazine. In early April 1940 Halder had a secret meeting with Carl Friedrich Goerdeler who asked him to consider a putsch while the Phoney War was still on hoping that the British and French were still open to a negotiated peace. Davies II in The Myth of the Eastern Front (Cambridge University Press 2008) argue that after 1945 Halder played a key role in creating a false and mythic view of the Nazi-Soviet war in which the Wehrmacht was largely blameless for both Germany's military defeat and its war crimes.

Franz Halder (30 June 1884 – 2 April 1972) was a German General and the chief of the OKH General Staff from 1938 until September 1942 when he was dismissed after frequent disagreements with Adolf Hitler. In William Shirer's The Rise and Fall of the Third Reich Halder's diary is cited hundred's of times.