This study presents a theoretical model of state security policy choice under varying conditions of external threat and domestic political competition. This model specifies a set of conditions associated with state capability, governmental structure and external threat that determine the levels and patterns of state resource allocation and redistribution. Domestic and international arenas are linked into an inclusive political environment. As politics is a reflection of competition for resources, all policy choices reflect decisions to allocate and distribute resources for a variety of goals. Given this interaction of domestic and international political spheres in the resource tradeoff dynamic, three issue areas are emphasized: national security, the maintenance of political position, and domestic political requirements. Instead of examining policy behavior from a static perspective, the model addresses changing conditions and how these conditions influence resource allocation and policy behavior. The model produces a number of expectations about state security behavior. In particular, external threat is hypothesized to increase resource allocation for security policies as well as increase cohesion within states. Conversely, as threat diminishes, domestic institutional factors return to prominence. Competition for the domestic allocation of resources increases. The validity of the model's expectations is assessed through the empirical examination of military expenditure levels, the formation of military alliances and foreign policy substitution efforts. Annual data (1816--1985) for all states in the international system is used in evaluation. A number of statistical tests, particularly maximum likelihood and cross-sectional time series techniques, are applied to the theoretical expectations. The model receives a great deal of empirical support. States do react to external threat and allocate resources for the development of security policy. As threats dissipate, domestic political preferences arise forcing resources to be reprioritized across the issue areas. Five principle findings emerge from the various analyses: (1) security policy is rarely static as decision-making environments are often in a state of flux; (2) threat motivates security policy; (3) internal political structures influence through institutional and resource allocation constraints; (4) the domestic stability of a state affects its security behavior; and (5) time and evolution of the international system influence individual state security.