Trench warfare
Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition. Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side that was able to commit the last reserves to the Western Front.
Gloucestershire Regiment in World War I
On the Western Front, hostilities commenced 2 August 1914 with the German invasion of Luxembourg and Belgium, designed to envelop Paris in a right sweep that avoided the most heavily defended French territory. The French, whose main effort was directed towards Alsace and Lorraine as a prelude to an invasion of Germany, were thrown onto the defensive on their left flank, which included one cavalry and four infantry divisions of the British Expeditionary Force. At the end of a two-week retreat from Mons the French managed to stop the Germans on the outskirts of Paris in the First Battle of the Marne. German forces retreated to the River Aisne and dug in, the first act of trench warfare that was to dominate the war.