The countries were handcuffed by treaty obligations to come to the aid of their allies in case of war. Russia was the only country who could have localized the war in the Balkans by not mobilizing in support of Serbia. Once Russia mobilized the war was on auto pilot. German war plans called for a quick campaign to defeat France like in 1870 before turning on the slower mobilizing Russia.
But by going through Belgium, that brought in the Brits, and subsequently the US, into the fight.
Still, there were cavalry attacks by Cossack squadrons on German border villages reported as early as 30th of July.
The Russian army had partially mobilized against Austria- Hungary, and Germany was the latter‘s ally. Emperor Wilhelm ll. pleaded on the same day with his cousin the Tsar to stop the mobilization, but the latter replied that there was nothing he could do any more, and that God bless him.
Witnesses to President Poincare’s state visit on the 20 th of July 1914 claim that there was a raucous celebration of Russian and French military officers, and cheers were raised to “Next year in Berlin! Hahahahaha!”
Doesn’t sound too peacelike, I should say.