German invasion of Belgium (1914)

Battle context

The German invasion of Belgium on 4 August 1914 was a pivotal opening act of World War I, directly triggering British entry into the conflict. Belgium had declared its intent to uphold neutrality on 24 July, and when the German ultimatum of 2 August demanding passage rights was rejected, Germany declared war and crossed the border, simultaneously launching the Battle of Liège. Britain's guarantee of military support to Belgium upon that refusal brought a major industrial and naval power into the war against Germany, fundamentally altering the strategic balance. The invasion also confirmed that the war would not be confined to the Franco-German frontier, forcing a multi-front coalition response from the outset. German forces numbered roughly 750,000 against a Belgian force of 220,000, with combined casualties of approximately 50,000 in the opening phase, signaling the scale of attritional warfare that would define the conflict.