Also the Germans knew that Russia was quickly modernizing, and if they ever wanted to fight Russia, it was “now or never”.
A lot like us and the Chinese.
That’s true the Germans did know Russia was modernizing quickly. The Germans were their largest investor!
Russia started mobilizing. The Germans learned of it and since their defense depended on speed (they had to knock out France before Russia could fully mobilize) Wilhelm talked to Nicholas I and told him Russian mobilization would put him in an impossible situation and begged him not to do it. Nicholas assured Wilhelm that he would not mobilize on Germany’s border.
The Russian generals then told Nicholas that they had no plan for partial mobilization and it was therefore all or nothing. They chose to mobilize everywhere knowing full well that would force Germany to go to war as a matter of national survival. I emphasize the word “chose”. They didn’t have to. They had no defense treaty with Serbia which was the aggressor in the whole thing.