The actual beef was between Austria and Serbia, it was the web of treaty obligations that caused all the trouble.
Serbia was allied with Russia while Germany was committed to assisting Austria, but Russia had treaty with France that committed them to fight whether they wanted to or not. Knowing the quality of their foes Germany had decided that they could knock France out quick then consolidate their forces in the East.
But the Shliefen plan's violation of neutral Belgium dragged in England who had no solid treaty with France, but had signed a treaty guaranteeing Belgian Neutrality.
In the end, Russia and Austria were the first 2 countries knocked out of the war, leaving it to the allies they had each sucked in to decide the matter.
What cost so much blood was that the equipment of the day was far in advance of both the tactics and communications capabilities of the day.
For example every one knows how the Machine gun mowed down ranks of infantry, but very few understand that once an attack was launched there was no way to stop it. Generals launched their divisions into a fog of smoke and dust and then waited to see where the next days morning report would come from.There were no portable radio's, troops had to march in close formation in order for their Officers to be able to direct them.
The saddest part is that the tactics HAD been developed. The Japanese showed the way in their 1905 war against Russia.
England had USED looser formations against the automatic weapons of the Boers in Africa.
But those were Colonial wars, lessons learned there didn't count in civilized warfare.