In 1914 the Belgian Army had six infantry divisions (43,000 men), with 115,000 in reserve. This did not provide enough men to staff Belgium's fortresses on the country's border and the German Army quickly overwhelmed these defences in August 1914. King Albert I, the commander-in-chief of the Belgian Army withdrew his forces and with the help of the British Expeditionary Army and the French Army, was able to hold a line just inside western Belgium.

King Albert was forced to move his government to Le Havre in France. The Germans now ruled most of Belgium and over the next few years was accused of carrying out atrocities against the civilian population.

Conscription of men in the small part of Belgium under Allied control raised the average strength of the Belgian Army to 170,000 men. A total of 267,000 men served in the army in the First World War, of whom about 54,000 were wounded and 14,000 killed.