The British Expeditionary Force (BEF) was the name given to the British Army sent to France and Belgium during the early stages of World War I. Established in 1914, its primary role was to support the Allied Powers against the advancing German Army. The BEF played a crucial part in several key battles, including the Battle of Mons and the First Battle of Ypres. Initially composed of professional soldiers, the BEF faced significant challenges, including supply shortages and heavy casualties. Over time, it expanded to include volunteers and conscripts, adapting to the demands of trench warfare. The BEF's experiences laid the groundwork for modern military strategies and tactics.