British Expeditionary Force (BEF), the home-based British army forces that went to northern France at the start of World Wars I and II in order to support the left wing of the French armies. The BEF originated in the army reform of 1908 sponsored by Richard Burdon (later Viscount) Haldane. Prior to this reform, it had been customary in the British army to ship off individual units and organize them into brigades or larger units when they had arrived at the theatre of operations. But by the first decade of the 20th century, in the light of Britain’s treaty obligations