A origem de todos os males do séc.20: comunismo, fascismo, nazismo, social-democracia, status-quo instáveis - e "o suicídio da civilização cristã"
Wikipedia: July crisis and declarations of war
After the assassination of Archduke Franz Ferdinand on June 28, 1914, Austria-Hungary waited for 3 weeks before deciding on a course of action, because most soldiers were on leave to help gather the harvest. On July 23, assured by unconditional support of the Germans should war break out, the empire sent the July Ultimatum to Serbia, which demanded, among other things, that Austrian agents would be allowed to take part in the investigation of the murder, and that Serbia would take responsibility for it. Emboldened by the promise of Russian support, the Serbian government accepted all the terms, except that of the participation of the Austrian agents in the inquiry, which it saw as a violation of its sovereignty. Breaking diplomatic relations, the Austro-Hungarian Empire declared war on Serbia on July 28 and proceeded to bombard Belgrade on July 29. On July 30, Austria-Hungary and Russia both ordered general mobilization of their armies.
The Germans, having pledged their support to Austria-Hungary, sent Russia an ultimatum on July 31 to stop mobilization within 12 hours. On August 1, with the ultimatum expired, the German ambassador to Russia formally declared war. On August 2, Germany occupied Luxembourg, as a preliminary step to the invasion of Belgium and the Schlieffen Plan (which was rapidly going awry, as the Germans had not intended to be at war with a mobilized Russia this quickly). The same day, yet another ultimatum was delivered to Belgium, requesting free passage for the German army on the way to France. The Belgians refused. At the very last moment, the Kaiser Wilhelm II asked Moltke, the German Chief of General Staff, to cancel the invasion of France in the hope this would keep Britain out of the war. Moltke, horrified by the prospect of the utter ruin of the Schlieffen Plan, refused on the grounds that it would be impossible to change the rail schedule—“once settled, it cannot be altered” . The question of whether such a radical change in Germany’s plans would have indeed been possible was the subject of much dispute. When Moltke’s reply was revealed after the war to General von Staab, Germany’s Chief of the Railway Division, he saw it as an affront to the capabilities of his unit, and proceeded to write a book proving such a change was indeed possible. On August 3, Germany declared war on France and invaded Belgium on August 4. This act—violating Belgian neutrality to which Germany, France, and Britain were all committed to guarantee—prompted Britain, which had been neutral, to declare war on Germany on August 4. Matthias Erzberger, the Reichstag deputy, later testified that six months after the outbreak of war, Moltke admitted that attacking France first was a mistake and that “the larger part of our army ought first to have been sent to the East to smash the Russian steamroller” .