When Germany lost World War II in 1945, they probably never dreamed this would occur because they were so confident in their abilities. Initially the country started off strong in the War during 1939 at the Invasion of Poland, and it was not until 1943 they began to falter.
Could have Germany won World War II? With a little hindsight and avoiding disastrous military blunders they could have written history much differently than we currently know it. The unification of Germany and Austria, and the taking of Czechoslovakia went like clock work. At the strategic and operational levels the invasion of Poland was flawless.
So what went so wrong for the new German Empire?
*Keeping allies in check
Spain: For the short term, signing the non-aggression pact with the Soviet Union allowed Germany to take half of Poland without having to face the weigh of their military. The immediate consequence was the loss of Spain as an ally. Frank Franco had fought the Soviets army in proxy during the Spanish Civil War.
Franco was not about to stay aligned to any country with a treaty to the USSR. Beginning able to maintain the alliance with Spain, bring it in as an Axis country would have closed off the Mediterranean of to the Allies. Once France had fallen the Axis would have controlled both the North and Southern approaches to the Mediterranean. This would have allowed all of Northern Africa to be captured.
Japan: The greatest blunder committed by Germany was not keeping Japan from attacking Pearl Harbor, thus bringing the United States into the War. Up to this point, the United States was generally neutral, but providing some aid to the Allies.
A history without Pearl Harbor would have delayed the U.S. entering the war and would have reduced its involvement. Peace movements in the U.S., like America First would have tempered the support of the war. The less than total war mentality would have given the Axis powers the breathing room they needed to take on the Allies one at a time as opposed to all at once.
*Invasion of Crete
British Intelligence fed the German Empire faulty information about the movement to fortify the Island of Crete and the Mediterranean. In response Germany invaded the Island of Crete with airborne Division and a Alpine Elite Division (relegated to an air-land element).
In the end the invasion was successful and reaffirmed the ability of vertical envelopment, but at a cost. The two divisions were shattered by the attack, the sea tail supporting airborne forces was caught by a British task force and most ships were lost and many of the air transports were wreaked on the small Crete airfields.
This resulted in fewer forces available for other operations needing an elite force and the German high command was so shocked by the losses they banned all future large airborne/air land operations.
*Hitler's changing objectives in USSR
During Operation Barbarossa Germany had three primary objectives:
1. The oil fields in the Caucus
2. Moscow
3. Stalingrad
The initial stages of the plan took huge swatches of land and destroyed whole Soviet Armies. The issue arose was when Germany, like Napoleon before, stretched their logistics lines to the breaking point and start started to run into heavy resistance. The German command started to move large units from supporting one objective to another, burning valuable resource that was getting harder to support.
If Hitler had reduced the changes in Operation Barbarossa and focused on the resources Germany needed to continue the war, the three Armies could have gained and held the land vital to Germany's future and capability to defeat the Soviet juggernaut.
*Death squads in USSR
Following many of the German Army Groups in the Soviet Union was SS death squads set to start the elimination of non-Germans and prepare for German settlers in the new Germany. Prior to these death squads the German s were seen as liberators from the brutality of Stalin. These Death Squads turned the locate sediment back to supporting the USSR.
Without these Death Squads, Germany would have had a huge population to draw resources from, to include nearly whole Armies will to fight against Stalin. These extra units many have shifted the German's Eastern front in their favor able to gain all of their objectives and taking the Soviet Union out of the war.
*Delaying long term military technology projects
In 1939 all programs that did not produce a product was put on hold to support current programs like tank and aircraft production. This resulted in the delay of development of long range heavy bombers, the jet and advanced weapons like the V-1, V-2, ground to air missile and the Atomic Bomb. If these had been developed and placed into production prior to the last year of the war, it may have ended differently.
These are some of the most critical blunders committed by the Third Reich. If only planning to maintain a greater European empire they may have been successful and the Cold War may have been the US vs. new German Empire. The U.S. with a weakened U.K. and few NATO allies against all the resources of Europe and Russian superpower allied to a combat ready Empire of Japan.