This paper re-examines the immediate causes of the escalation of the July Crisis in 1914 by analyzing Austria-Hungary’s increasing resolve to use military force against Serbia and the evolving nature of Russian mobilizations between 1908 and 1914. The July Crisis can be viewed as a continuation of the Bosnian annexation crisis and the First and Second Balkan Wars from 1908 to 1913. Many underlying or structural explanations for the outbreak of the First World War fail to account for the specific escalation in 1914, particularly because these factors remained largely unchanged between the crises of 1913 and the July Crisis of 1914. This article argues that the two most proximate causes of the war’s outbreak were, first, the heightened resolve of Austro-Hungarian leaders to use military force against Serbia in July 1914—a qualitative shift from the coercive diplomacy of previous Balkan crises —and second, Russia’s decisions regarding preparatory war measures and general mobilization between July 25 and July 30, which contrasted with its earlier trial or partial mobilizations. In highlighting these developments, the paper challenges the dominant German paradigm and emphasizes the interactions among Serbia, Austria-Hungary, and Russia as key drivers in the escalation of the July Crisis into the First World War.