This thesis explores the concept of defeat. Specifically, it seeks to answer, "How should air and ground forces work together to defeat an enemy fielded force?" This question is important to the military strategist for two reasons. First, the US increasingly relies on smaller combined-arms teams and joint employment to fight the nation's battles. Failure to defeat an adversary at the first opportunity may deplete friendly forces and erode domestic and international support to such an extent that tactical, operational, or strategic victory is unattainable. Second, today's smaller forces place a premium on economy of effort. A common understanding of how to apply force to create defeat is required to increase efficiency in attaining economic effects among the services. To answer the question, the definition of defeat is explored in some detail. Definitions found in various service doctrines and Trevor Dupuy's writings are examined. The result is a structural definition of defeat, from which to base the framework for the study. The causes of defeat are also investigated. From the writings of Carl von Clausewitz, Ardant du Picq, and J. F. C. Fuller, a theoretical basis is developed to understand the elemental causes of defeat. Service doctrines are also reviewed to ascertain current beliefs of the causes of defeat. From this exploration, a model of defeat is constructed. This model, however, would be incomplete without linking the external stressors applied by friendly forces and the internal dynamics of the enemy force. Thus, this study analyzes links via defeat mechanisms. Brigadier General Huba Wass de Czege offers a model of defeat mechanisms that closely matches the elemental causes of defeat and, thus, forms a basis of analysis for this study. To answer the central question, this thesis examines three campaigns: the fall of France in 1940, the Arab-Israeli Six-Day War of 1967, and the Gulf War of 1991.