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.
Artillery of World War I
The artillery of World War I was used primarily to counter the trench warfare that set in shortly after the conflict commenced, and was an important factor in the war, influencing its tactics, and operations, and being incorporated into strategies that were used by the belligerents to break the stalemate at the front. World War I raised artillery to a new level of importance on the battlefield.