Well, a very large share of the French wanted the war, and not only the elites. The education system, the army, had been propagandising about a revenge against the Germans since 1870.

Don't forget at the time nationalism had been a left-wing idea ; in 1870 the republicans were in favour of continuing the fight, against the monarchists and bonapartists who had agreed to an armistice.

Many events in France before the war can be understood as part of the war preparations against Germany : for example the Dreyfus affair started as a espionage scandal as Germany had gained access to secret artillery designs.

Un roi sans divertissement est un homme plein de misères