On 3 August the
Belgian government refused a German ultimatum and the British government guaranteed military support to Belgium if Germany invaded. Germany declared war on France, the British government ordered general mobilisation and Italy declared neutrality. On 4 August, the British government sent an ultimatum to Germany and declared war on Germany at midnight on 4/5 August, Central European time. Belgium severed diplomatic relations with Germany and Germany declared war on Belgium. German troops crossed the Belgian frontier and attacked
Liège. A week after the German invasion, German cavalry had been operating towards
Diest, which threatened the left flank of the army on the Gete. Belgian general headquarters chose Halen as a place to delay the advance and make time to complete an orderly retreat to the west. The Belgian Cavalry Division was sent from
Halen, to extend the Belgian left flank.