- System of Alliances: Germany had forged alliances with Austria-Hungary and Italy through the Dual Alliance and subsequent treaties. In response, France aligned with Russia in the Franco-Russian Alliance of 1894. The system of alliances meant that an attack on one country could potentially draw in its allies and escalate into a broader conflict.
- Violation of Belgian Neutrality: When World War I began in 1914, Germany violated the neutrality of Belgium by invading in order to reach France quicker. Belgium and Great Britain had agreements guaranteeing Belgian neutrality, so Britain entered the war to uphold this promise, triggering France's involvement as well.