Under a treaty of 1839 Great Britain was obliged to defend Belgium in the event of an invasion of its territory and accordingly, on the 3rd August, the British Government ordered a General Mobilisation. On the following day an ultimatum was despatched to Germany demanding a withdrawal of its troops from Belgium. By 11pm on that day, the 4th August 1914, no promise to withdraw had been received by the British Government and war on Germany was declared.