Operational art is the act of applying military art to the operational art of war. Operational art is usually carried out under the tenets of either attrition warfare theory or maneuver warfare theory. Attrition warfare stress numbers and combat power as ways to victory, with loss ratios and fractional exchange rates being the indicator of combat. Attrition is often called a ‘bottoms-up’ approach, as the strategic and operational level are ‘subordinate’ to the tactical level of warfare. Maneuver warfare theory, as stressed by figures such as Sun Tzu, Liddel Hart, and Simpkin, attempts to create victory by preemption, dislocation, and disruption. It relies on the intangibles of warfare, such as morale, and the ability of commanders to correctly understand and predict them. Its defenders see it as a 'top to bottom' approach, as battles serve campaigns, campaigns serve wars, and wars serve broad political and economic objectives. FM 100-5 is the doctrine of operational art for the US army. Although it and its defenders claim that it is based on the ideals of Maneuver warfare theory, critics, such as Robert Leonhard, have charged that it is an work of attrition theory. Most agree, however, that the later versions of it are based more on Maneuver warfare theory then the earlier versions.