During the First World War (1914–1918), trench warfare became common along the Western Front.
In this area of Belgium and Northern France, the Allied forces of France, Britain, Canada, and eventually the United States were engaged in prolonged military standoffs with German forces. To take shelter from machine-gun fire and artillery, soldiers on each side dug long ditches at the front lines in which they lived for weeks at a time.
Battles and raids required going over the top of the trench and crossing the area of land between enemy trenches known as no man's land, where soldiers might run into mines, barbed wire, or the decomposing bodies of their fellow troops. Due to the likelihood of being targeted by enemy machine guns, rifles, and grenades, both sides suffered an immense number of casualties. In the particularly gruesome Battle of Somme, British forces suffered 60,000 deaths on the first day of fighting.
Compounding the brutality of combat missions, life in the trenches was famously hellish. Disease spread easily due to the unsanitary conditions of the dugouts, and many soldiers experienced post-traumatic stress disorder (known at the time as shell shock) from living under constant bombardment.
Trench warfare became less common in subsequent wars due to advances in weapons technologies with the development of armored tanks and bomber planes.