[prof.h.mandingo]

True as far as you go. But you left out some details like “mobilization” and the problems associated with it. The Tsar and Kaiser Bill wanted to back out but were told they couldn't stop what was started. Actually they could have but they didn't have the balls to make the generals stop.
As far as grudges and wanting pay back lets not forget the French were itching to avenge an earlier defeat (Franco-Prussian War).
Of course the Germans thought they were going to win. You don’t go into war thinking you will lose.
You are correct about the Serbs giving them most of what they wanted but it was the Austrians who pushed for war.
Russia wouldn't mind getting a chunk of Turkey.
The truth is that many countries were itching for war for many years. The Germans happened to pull the trigger of a loaded gun that many countries were itching to pull.

[agere_contra]

The Germans happened to pull pulled the trigger of a loaded gun that many countries were itching to pull.

Please note my correction. The Germans didn't 'happen' to pull the trigger. The gun didn't go off in their hand.

World War One began because the Germans invaded Belgium and the Austro-Hungarian Empire invaded Serbia.

The Germans fired the guns of August. They chose to begin what became World War One. Only they - and Austro-Hungary - are to blame.