Italy required help in Greece and North Africa against their common foe because they where failing miserably. Germany made USA turn into a common foe themselves. Besides, Japan made sure the UK had to transfer more attention and material off too the Pacific, making it easier for Germany. They took away a lot of resources from the British as well(oil). That is, untill the USA took it over for them.
Also, Hitler was under no obligation whatsoever to declare war on the United States after Pearl Harbor. He did it entirely on his own initiative, and let his anti-Semitism, anti-capitalism, and personal hatred of Roosevelt get the better of him. That said, the U.S. would have entered the European War in early 1943 at the latest, but that was the critical year in which Germany had to knock both the British and the Soviets out of the war, or else get drawn into a war of attrition in which it was seriously outmatched.
Italy clearly hurt Germany more: it was a sink of resources and equipment, and Mussolini's adventurism opened up several fronts that forced Germany to dive in and save him, to the point of delaying Barbarossa, Hitler's entire life goal, and reason for starting the war in the first place.
So what you guys are saying is that it was Germany's fault that they were at war with the United States because they declared War on their own?
Well the Italians didn't ask for Germany's help in North Africa and Greece. The Germans did that on their own too.
What Hitler should have done is let Japan and the Americans fight a war in the Pacific, and not declare war on them. They should have also let the the Italians fall in their war in North Africa. At the very least it would divert some of the British forces away from Germany for a while.