This study examines the propensity of internally weak states to form alliances with or against threatening powers. Drawing upon insights from neoclassical realism, the study proposes a 'resistance' model of weak state alliance formation and tests the model using cases drawn from the states of the former Soviet Union. The study examined the performance of resistance theory explanations when compared to explanations drawn from the dominant theory of alliance formation, Balance of Threat, as well as a generally accepted theory of weak state alliances, Capitulationist theory The study finds that the leaders of weak states are particularly susceptible to the influence of 'critical constituencies' within their states---those social and political forces upon which weak regimes most depend for continued authority. The reliance of weak leaders on these narrow segments of society often precludes alliances with threatening external powers whose demands are at odds with the values of the critical constituency Ultimately, internally weak states were found to be no more willing to be coerced into binding alliance agreements than were similarly threatened states with greater levels of internal cohesion. This finding was inconsistent with Capitulationist theory, consistent with Balance of Threat but best explained by resistance theory / acase@tulane.edu

Cette thèse exploite les liens profonds entre la physique des systèmes quantiques locaux, les propriétés non locales de leurs états fondamentaux et le contenu en information de ces états. Les deux premiers chapitres sont consacrés à l’application des systèmes quantiques locaux pour les fins d’une tâche informationnelle précise, soit le calcul quantique. Au terme d’un bref survol de la théorie, nous proposons un patron pour le calcul quantique universel et évolutif pouvant être réalisé sur une grande variété de plateformes physiques, et démontrons qu’il est particulièrement résilient face à un bruit anisotrope. Les quatre derniers chapitres sont pour leur part consacrés à l’approche informationnelle des systèmes quantiques à corps multiples. Nous décrivons les principales propriétés des corrélations et de l’intrication dans les états fondamentaux des systèmes de dimensions réduites les plus courants, en distinguant systèmes non critiques et systèmes critiques. Nous montrons que ces propriétés sont fortement modifiées par la présence de frustration géométrique dans les chaînes de spins. Enfin, nous réalisons une analyse exhaustive des corrélations et de l’intrication dans les états fondamentaux de deux théories quantiques de champs non triviales. / This thesis exploits the deep connections between the physics of local quantum systems, the nonlocal features in their ground states, and the information content of these states. The first two chapters are dedicated to the application of local quantum systems for the purpose of a definite information-theoretical task, namely quantum computation. After a brief survey of the theory, we propose a scheme for scalable universal quantum computation that, we argue, could be implemented on a wide variety of physical platforms, and show that it is particularly resilient to anisotropic noise. The last four chapters are dedicated to the information-theoretical approach of many-body quantum systems. We describe the main properties of correlations and entanglement in the ground states of the most common low-dimensional many-body systems, distinguishing between noncritical systems and critical ones. We show how these properties can be dramatically modified by the presence of geometric frustration in spin chains. Finally, we perform an intensive study of correlations and entanglement in the ground states of two nontrivial one-dimensional quantum field theories.