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.
United Kingdom of Great Britain and Ireland
Britain entered the war to protect Belgium from German aggression, and quickly assumed the role of fighting the Germans on the Western Front, and dismantling the overseas German Empire. The romantic notions of warfare that everyone had expected faded as the fighting in France bogged down into trench warfare. Along the Western Front the British and French launched repeated assaults on the German trench lines in 1915–17, which killed and wounded hundreds of thousands, but made only limited gains. By early 1916, with number of volunteers falling off, the government imposed conscription in Britain (but was not able to do so in Ireland where nationalists of all stripes militantly opposed it) in order to keep up the strength of the army. Industry turned out munitions in large quantities, with many women taking factory jobs. The Asquith government proved ineffective but when David Lloyd George replaced him in December 1916 Britain gained a powerful and successful wartime leader.