Belgium's entry into the war made matters more complicated for the allies. Initially, this war was seen by many in the world as a tragic response of Austro-Hungarian aggression into Serbia. The late Serbian King Peter I had made it seem like their requests would violate his sovereignty as an independent ruler.
However, as more and more hidden secrets were revealed, Serbia and its royal family started becoming the villains from the perspective of those neutral nations which sat by and watched as Europe burned in the background.
In addition to this, France's violations of Luxembourgish and Belgian neutrality was seen as a flagrant and aggressive violation done without any potential just cause. At least the Austro-Hungarians had a valid casus belli to declare war on the Serbians.
