Why did Britain enter World War I?

Great Britain entered World War I on August 4, 1914, primarily in response to the German invasion of Belgium.12

While the British cabinet was initially divided regarding the escalating conflict in the Balkans, the German military’s decision to violate Belgian neutrality—which Britain was committed by treaty to uphold—provided the immediate catalyst for the declaration of war. Beyond this specific obligation, Britain’s entry was driven by broader strategic concerns regarding the balance of power in Europe. British policymakers feared that if they remained aloof, Germany might achieve continental hegemony, potentially placing the German fleet in the English Channel and threatening British security.13

This decision followed years of rising tensions, including a naval arms race with Germany and the formation of the Triple Entente, which aligned Britain with France and Russia. Ultimately, the combination of treaty obligations to Belgium and the necessity of preventing a hostile power from dominating the European coast compelled Britain to join the conflict.143