Manifest Destiny et l'expansionnisme américain au XIXe siècle

Analyze the ideological foundations of 'Manifest Destiny' during the $19^{th}$ century. Discuss how this concept, popularized by John O'Sullivan in $1845$, shaped the American ethos of the 'Frontier'. Critically evaluate the tension between the narrative of spreading democratic values and the historical reality of territorial acquisition, specifically addressing the impact on Indigenous populations and the legal justification of the era.