Given the alignment of the alliances, some declarations of war awaited only the proper moment. Certainly this was true of Austria-Hungary’s declaration of war against Russia, where the Austro-Hungarian general staff felt no need to pretend to be at war with Russia until both countries were a bit farther along into their military mobilizations.
By waiting until August 6, Austria-Hungary hoped to confuse Russian military planners: should they prepare for an Austro-Hungarian army or not? Given the size of Russia’s armies, the effect of this confusion would be slight, if it existed at all, but with little risk with a potentially great reward, the action was worth their delay in declaring their solidarity with Germany against Russia.
Serbia also declared war against Germany on this day, though their reasons are a bit more perplexing: Serbia did not share a border with Germany, and indeed there were hundreds of miles of Austria-Hungarian territory (their primary enemy) separating the two countries. Perhaps Serbia merely wished to show its solidarity with Russia, and perhaps it wanted to justify any German casualties that might occur if they somehow appeared on the Serbian front.
August 6 also saw the first major assault on the fortified Belgian town of Liège by the Germans. A special force of over 30,000 troops assaulted some of the strongholds after a demand for surrender had been rejected, but they were repulsed.
Meanwhile, the Germans had crossed through Luxemburg and were also laying siege to Longwy, France. Victory here, as in Liège, would open up an indispensible avenue through which the German forces would pour into France.