The German invasion of Belgium was a military campaign which began on 4 August 1914. Earlier, on 24 July, the Belgian government had announced that if war came it would uphold its historic neutrality. The Belgian government mobilised its armed forces on 31 July and a state of heightened alert was proclaimed in Germany. On 2 August, the German government sent an ultimatum to Belgium, demanding passage through the country, and German forces invaded Luxembourg. Two days later, the Belgian government refused the demands and the British government guaranteed military support to Belgium. The German government declared war on Belgium on 4 August, troops crossed the border and began the Battle of Liège.
German military operations in Belgium were intended to bring the 1st, 2nd and 3rd armies into positions in Belgium from which they could invade France, which, after the fall of Liège on 7 August, led to sieges of Belgian fortresses along the river Meuse at Namur and the surrender of the last forts. The government abandoned the capital, Brussels, on 17 August and after fighting on the Gete river, the Belgian field army withdrew westwards to the National Redoubt at Antwerp on 19 August.