Another source, albeit from an american perspective,
Four Days in December: Germany's Path to War With the U.S.
And this is source material of an even more dubious origin, but it is a faithful translation of Hitlers address to the Reichstag
Hitler Declares War on the United States
This in my opinion is the relevant part of hitlers address to the reichstag. Typical of Hitlers speeches, it is a rambling confused affair, full of half truths and outright lies, but it also reveals what he was thinking at the time of the declaration.
"We have seen what the Jews have done in Soviet Russia. We have made the acquaintance of the Jewish Paradise on earth. Millions of German soldiers have been able to see this country where the international Jews have destroyed people and property. The President of the U.S.A. ought finally to understand-I say this only because of his limited intellect-that we know that the aim of this struggle is to destroy one State after another. But the present German Reich has nothing more in common with the old Germany. And we, for our part, will now do what this provocateur has been trying to do so much for years. Not only because we are the ally of Japan, but also because Germany and Italy have enough insight and strength to comprehend that, in these historic times, the existence or non-existence of the nations, is being decided perhaps for ever. We clearly see the intention of the rest of the world towards us. They reduced Democratic Germany to hunger. They would exterminate our social things of today. When Churchill and Roosevelt state that they want to build up a new social order, later on, it is like a hairdresser with a bald head recommending an unfortunate hair-restorer. These men, who live in the most socially backward states, have misery and distress enough in their own countries to occupy themselves with the distribution of foodstuffs.
As a consequence of the further extension of President Roosevelt's policy, which is aimed at unrestricted world domination and dictatorship the U.S.A. together with England have not hesitated from using any means to dispute the rights of the German, Italian and Japanese nations to the basis of their natural existence. The Governments of the U.S.A. and of England have therefore resisted, not only now but also for all time, every just understanding meant to bring about a better New Order in the world. Since the beginning of the war the American President, Roosevelt, has been guilty of a series of the worst crimes against international law; illegal seizure of ships and other property of German and Italian nationals were coupled with the threat to, and looting of, those who were deprived of their liberty by being interned. Roosevelt's ever increasing attacks finally went so far that he ordered the American Navy to attack everywhere ships under the German and Italian flags, and to sink them-this in gross violation of international law. American ministers boasted of having destroyed German submarines in this criminal way. German and Italian merchantships were attacked by American cruisers, captured and their crews imprisoned. With no attempt at an official denial there has now been revealed in America President Roosevelt's plan by which, at the latest in 1943, Germany and Italy were to be attacked in Europe by military means. In this way the sincere efforts of Germany and Italy to prevent an extension of the war and to maintain relations with the U.S.A. in spite of the unbearable provocations which have been carried on for years by President Roosevelt, have been frustrated. Germany and Italy have been finally compelled, in view of this, and in loyalty to the Tri-Partite act, to carry on the struggle against the U.S.A. and England jointly and side by side with Japan for the defense and thus for the maintenance of the liberty and independence of their nations and empires.
The Three Powers have therefore concluded the following Agreement, which was signed in Berlin today:
"In their unshakable determination not to lay down arms until the joint war against the U.S.A. and England reaches a successful conclusion, the German, Italian, and Japanese Governments have agreed on the following points:
Article I. Germany, Italy and Japan will wage the common war forced upon them by the U.S.A. and England with all the means of power at their disposal, to a victorious conclusion.
Article II. Germany, Italy and Japan undertake not to conclude an armistice or peace with the U.S.A. or with England without complete mutual understanding.
Article III. Germany, Italy and Japan will continue the closest cooperation even after the victorious conclusion of the war in order to bring about a just new order in the sense of the Tri-Partite Pact concluded by them on the 27th September 1940.
Article IV. This Agreement comes into force immediately after signature and remains in force as long as the Tri-Partite Pact of 27th September 1940. The Signatory Powers will confer in time before this period ends about the future form of the co-operation provided for in Article III of this Agreement.""