World War One WAS deliberately started:
Germany had for decades considered the advantage over France gained by the !870-71
Franco-Prussian War to have been insufficient, and had been spoiling for a chance to
obtain greater advantage, through war if need be.
Also, Germany supported Austrian expansion in the Balkans, and after Archduke Ferdinand
was assassinated encouraged Austria to go to war over it, knowing that Russia would almost
surely be drawn in on Serbia's behalf, and France along with it, since France and Russia had
a military treaty. Germany could have averted war by refusing to endorse Austria's demand,
which no sovereign nation could agree to, that Serbia permit operation of Austrian
courts martial on Serbian soil. Instead Germany encouraged Austria from the start of the
crisis, guaranteeing war.
As to the objection that Russia and France might also have taken steps to avoid war, such
as letting Austria have its way with Serbia, perhaps that is true. However, the issue raised
by OP was whether starting the war was deliberate, and it is reasonable to consider the word
"deliberate" to mean that war was, from the start of the crisis, THE desired outcome. It certainly
was for the governments of August 1914 Germany and Austria! But I do not believe the same
could be said for Russia and France.