There was an alliance and Germany was bound to defend its ally
just like the deal between Britain and its allies and the fight was on.
Germany did not start WWI they just paid for it in the long run.
You need to study a little history.
Austria-Hungary wanted to invade Serbia.
They feared the Russians.
They went to the Kaiser asking for support.
The Kaiser told him he would back them no matter what. THAT makes him guilty.
Austria Hungary issues a completely unacceptable ultimatum to Serbia, then invades.
Russia mobilizes to aid her ally Serbia.
Here is where it gets complicated...........France and Russia are allies. Germany fears modern France, but not slow Russia. To avoid a two front war, the German Schlieffen Plan calls for Germany to invade FRANCE if Russia mobilizes against her........the idea is crush France quickly, then turn to face the Russians.
Germany invades France through the lowlands, despite being warned by Great Britain to stay out.
Great Britain moves to defend her allies.
YES, Germany was at fault.