The interesting issue here was GermanyŪs
decision to make formal declarations of war, over the objections of some
of its military advisers. On 2 August 1914, Admiral Tirpitz complained
repeatedly that a declaration of war on France was not necessary, because
it would give an aggressive flavor to the German actions and cast all the
guilt on them. However, Chancellor Bethmann-Hollweg insisted, saying
that it was necessary as part of the justification for the march through
Belgium the following day. Furthermore, the Hague Convention on the
conduct of hostilities required that declarations of war be given before
the commencement of hostilities. However, as Tuchman describes in
Chapter 8 of her book The Guns of August, Tirpitz was still not
satisfied, fearing that the move through Belgium, ža pure emergency measure,Ó
would wrongly be cast žin the fateful light of a brutal act of violence.Ó
Thus, this obligation formally to declare war before waging war against
an enemy was respected by all parties to the conflict.
The international legal obligation to declare war before commencing hostilities comes from the Hague Convention Relative to the Opening of Hostilities (entry into force: 26 January 1910). Article 1 provides that "The Contracting Powers recognize that hostilities between themselves must not commence without previous and explicit warning, in the form either of a reasoned declaration of war or of an ultimatum with conditional declaration of war." Article 2 gives the procedural requirements necessary to comply with Article 1: "The existence of a state of war must be notified to the neutral Powers without delay, and shall not take effect in regard to them until after the receipt of a notification, which may, however, be given by telegraph. Neutral Powers, nevertheless, cannot rely on the absence of notification if it is clearly established that they were in fact aware of the existence of a state of war."
For the most complete list of who declared war on whom and when, go to http://users.tibus.com/the-great-war/bellig01.htm.
Unfortunately, I could not find any Internet links directly related to the debate within the German government over whether to declare war or not. Thus, if this issue intrigues you, you will have to pursue it through general library resources.