Despite their many successes, Roman leaders continually struggled with indiscipline in their own ranks as they battled Rome's opponents. Desertion and defection were steps that soldiers often undertook to avoid their obligated service. Previous scholarship has largely overlooked this aspect of Roman warfare. This dissertation analyzes why Roman soldiers began turning to desertion and defection throughout the Republican period. Such cases were generally rare in early Rome, but the expanding responsibilities and hardships of warfare in the Middle Republic caused them to rise, as did the sizeable growth of the Roman community. The civil wars of the Late Republic saw especially high cases of such acts, as generals incentivized defections in their opponents ranks. Roman desertion was not unique, but a common occurrence in ancient warfare. This dissertation also addresses how Romans capitalized on desertion and defection in warfare. The Second Punic War offers an example of how Rome achieved victory by encouraging defection in its enemy's alliances. Romans also relied heavily on defectors as a source of intelligence and as a tool in siege warfare. The moral forces of commitment, discipline, dissatisfaction, and desertion were often as important as the tactics and technologies of the participants in Rome's wars.

The expansionist agenda of the Polk administration culminated in the War with Mexico. The capture of Mexico City in September 1847 left the United States Army with the unprecedented task of occupying an enemy capital for an extended period. After the initial theaters of operation proved unable to secure a peace, Maj. Gen. Winfield Scott commenced a campaign to take central Mexico including the capital city. In March 1847, an army of 11,000 soldiers under Scott landed at Vera Cruz. In six months, Scott's army marched over 250 miles and won five major battles. In mid-September, Scott took Mexico City. Throughout the campaign, Scott attempted to implement a pacification plan in an effort to prompt Mexico to open peace negotiations. Concern for his army weighed heavily on him as he faced unprecedented challenges in occupying Mexico City after its capture. The United States simply had almost no experience in the ramifications of fighting a foreign war, other than a few brief small-scale incursions onto foreign soil at Tripoli in 1805 and in British Canada. The difficulties that arose for Scott from the situation in Mexico were frustrating. Scott pacification plan used conciliation, coercion, and force on Mexico's army and people …