The article explores how American isolationism and the idea of "Manifest Destiny" influenced pre-World War I diplomacy. Isolationism initially shaped America's view of itself as separate from the rest of the world, while Manifest Destiny, rooted in Protestant beliefs, guided interactions with other nations. These ideologies coexisted, with isolationism dominating until America emerged as a global player after World War I. The relationship between isolationism and Manifest Destiny impacted foreign policy decisions, raising questions about their roles in shaping American history.