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.
Mường Thanh Valley
The First Indochina War began on December 19, 1946 as a battle between the French trying to regain their colonial claims in Vietnam and the Viet Minh attempting to gain control of the area. In the early 1950s Viet Minh forces were making steady advancements on French-controlled parts of Northern Vietnam. By late 1952 much of the Red River Delta was under Viet Minh control. Due to its proximity to supply routes from China, the Mường Thanh Valley region was vital to the survival and support of the Viet Minh. The French forces in Vietnam under General Henri Navarre sought to occupy Dien Bien Phu. This would allow them to cut off an important supply route to the Viet Minh and also help them to fight against a Viet Minh offensive in Laos.