War of Attrition
A war of attrition is a war in which the competing sides seek to win by exhausting the enemy's resources, rather than by a decisive battlefield victory. Such wars tend to be long-lasting, with relatively static battlefronts. Probably the best modern example of a war of attrition was the conflict on the Western Front in the First World War (1914-1918); another is the Iran-Iraq War (1980-1988).
No war is by intention a war of attrition; rather, the aggressor almost invariably expects a swift victory (Germany invading Belgium and France in 1914, Germany invading the USSR in 1941, the Allies invading Italy in 1943, Iraq invading Iran in 1980), and it is only once such hopes are disappointed that a war takes on an attritional character.