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.
Howitzer
The onset of trench warfare after the first few months of the First World War greatly increased the demand for howitzers that gave a steep angle of descent, which were better suited than guns to the task of striking targets in a vertical plane (such as trenches), with large amounts of explosive and considerably less barrel wear. The German army was well equipped with howitzers, having far more at the beginning of the war than France.