Germany was first, but both sides were looking for an excuse to start a war.
'The nation that...can still be held least responsible for the outbreak of the war is France. This is so even if we bear in mind all the revisions of historical judgments, and all the revisions of these revisions, to which we have now been treated....The French, in 1914, entered the war because they had no alternative. The Germans had attacked them. History can be very simple at times.[1]'"
[0]https://en.wikipedia.org/wiki/Joachim_Remak
[1]https://en.wikipedia.org/wiki/French_entry_into_World_War_I#...