Had Hitler not declared war on the U.S. Germany still could’ve won the war while fighting on two fronts against only England and Soviet Russia.
You have to remember that Rommel was on the verge of having total control of North Africa until the U.S. got involved. Had Rommel only the British to oppose him, he would’ve driven over the Suez, turned North into Turkey, and then connected with the Southern Armies on the Russian front perhaps even creating another Russian pocket while capturing vital oil fields in the spring of 1942. The next logical move for Rommel would’ve been to press Eastward and if not seize or destroy the Russian industry, cause enough of a hiccup in the supply lines to the Russian front that not enough ammunition, fuel, parts, or equipment would be available on the Russian front to stop a hard-pressed general advance against the Soviets.
One of the most fatal flaws on the Russian front was the destruction of the 6th Army at Stalingrad. In terms of manpower it was severe, but the magnitude of the effect on the morale of the German soldiers dwarfed the physical loss of Stalingrad and Field Marshall Von Paulus’ army.
Most incriminating to the Germans however, was the rampant behavior of rape, murder, and all-out thuggery of the SS divisions. Their absence would’ve greatly benefited the Germans with a fresh suply of willing peasants who will fight for the Germans against the Soviets and would be willing subjects after the Soviet Union was dissolved.
