How did Germany's invasion of Belgium bring Great Britain into World War I?

The German invasion of Belgium on August 4, 1914, was the decisive factor that brought Great Britain into World War I against Germany.12

While the British cabinet had been divided regarding the escalating international crisis, the German military’s decision to violate Belgian neutrality—which Britain was committed by treaty to uphold—provided the necessary impetus for the British declaration of war on the same day.32

This invasion was a core component of the Schlieffen Plan, a strategic maneuver designed to allow Germany to wage a two-front war by quickly defeating France before turning its forces toward Russia. By sweeping through neutral Belgium to bypass hardened French border defenses, the German army committed an unprovoked act of aggression against a neutral country, which ultimately solidified Britain's entry into the conflict.412