Although Adolf Hitler was an extremely successfully political entrepreneur and as the absolute ruler of Germany led the country to probably the most successful Quantensprung in civilian life, he was far more comfortable in the Army (and in the armed forces in general).
So it is no surprise at all that after the beginning of World War II, Adolf Hitler gradually began to devote himself almost exclusively to military issues, relying more and more on his subordinates (and ultimately on Martin Bormann) to handle the domestic policies of the country.
Overall, Adolf Hitler managed his country’s war effort during World War II to a much greater extent than any other national leader (with possible exception of Joseph Stalin).
By 1943, Bormann had de-facto control over all domestic matters which made him an acting Vice-Chancellor. After the invasion of the Soviet Union in June of 1941, Adolf Hitler spent most of his time at his military headquarters on the Eastern front, essentially performing but one government function – Commander-in-Chief of German Wehrmacht. Consequently, it would be appropriate to evaluate Adolf Hitler during the World War II strictly as a military commander.
From the functional performance perspective, it is appropriate to divide the whole World War II into two stages – successful, even highly successful (from September 1st, 1939 to December 4th, 1941) and disastrous (from December 5th, 1941 to April 30th, 1945 when Adolf Hitler committed suicide in the Führerbunker).
The first period was probably the most successful military campaign (actually, more than one military campaign) in the history of warfare. Hitler invaded, defeated and conquered Poland, France, Benelux countries, Denmark, Norway, Greece, Yugoslavia, Albania, Crete, territories of modern Ukraine, Belarus, Baltic countries, Moldova and a significant part of European Russia (overall about 40% of the population of the USSR found themselves under German control), destroyed just about all invasion army (the whole First Strategic Echelon of the Red Army) that was to attack Germany on June 23rd of 1941 (about 5 million men, 6 million rifles and machine guns, over 20,000 tanks, over 33,000 artillery pieces, 60,000 mortars, about 21,000 aircraft – just about everything the Red Army had on June 22nd) ultimately reaching the outskirts of Moscow.
There was only one battle that Hitler did not win but did not exactly lose either (Air Battle of Britain). He suffered just one setback – had to cancel Operation Sea Lion (amphibious invasion of Britain). Which could have actually been “a blessing in disguise” as this endeavor would have almost certainly ended in a total disaster.
During that period, Hitler committed just two blunders – occupied Crete instead of Malta (right before invading the USSR) and allowed Britain and Free French to evacuate over 338,000 Allied soldiers from French port of Dunkirk to the British territory (for the Allies it was a genuine Miracle at Dunkirk).
Adolf Hitler won all his battles in Europe (Soviet Union was a different story) by using the same approach, method and procedure. First, he had a crystal clear vision of what he wanted to achieve – force his opponent to surrender and subsequently occupy his territory.
Second, he knew precisely how to do it – by destroying the armed forces and occupying the key strategic points and areas of the territory in question. Third, he knew perfectly well how to achieve this objective – by thoroughly planning and audaciously executing a daring blitzkrieg (lightning-fast war) which would last only for a few weeks. Inspiring, motivating, leading and, if necessary, managing his (often reluctant) generals.
And finally, the blitzkrieg always was a combined operation of land forces – motorized infantry, tanks, artillery – and Luftwaffe (occasionally supported by paratroopers that also belonged to the latter).
Hitler did not win the Battle of Britain because neither he, nor the top Luftwaffe commanders (Göring, Ritter von Greim and others), nor any other Wehrmacht generals for that matter had any idea on how to fight the offensive air war without the support of ground forces (it is far, far easier to fight a defensive air war than an offensive one).
Operation Sea Lion was doomed because “none of the above” knew how to conduct massive amphibious invasion. In addition, no one had any idea of what “victory over Britain” meant in practice.
Invasion and occupation of Britain was – for every practical purposes – impossible and there was no discernable way to force His Majesty’s Government to sign peace treaty with Germany on Hitler’s terms.
Adolf Hitler did not realize (probably at all, let alone in time) that he had a chance to achieve exactly that – by forcing the Allied forces at Dunkirk (whose morale and fighting spirit were already sufficiently low) to surrender and then use them as hostages in peace negotiations.
The conclusion is inevitable – Adolf Hitler could win only those battles (and wars) where (1) he had a clear vision of victory; (2) he knew the way how to achieve it; and (3) that way was a blitzkrieg – a lightning-fast attack of combined land and air forces (Army and Luftwaffe).
When one or more of these conditions was not present, Adolf Hitler could not win the war. That’s the one and only fundamental reason why he failed to defeat Britain.
And the Soviet Union.