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.
Trench warfare
A basic wire line could be created by draping several strands of barbed wire between wooden posts driven into the ground. Loose lines of wire can be more effective in entangling than tight ones, and it was common to use the coils of barbed wire as delivered only partially stretched out, called concertina wire. Placing and repairing wire in no man's land relied on stealth, usually done at night by special wiring parties, who could also be tasked with secretly sabotaging enemy wires. The screw picket, invented by the Germans and later adopted by the Allies during the war, was quieter than driving stakes. Wire often stretched the entire length of a battlefield's trench line, in multiple lines, sometimes covering a depth or more.