While America’s expansionist policy, adopted after the Spanish-American War, is commonly perceived as a diplomatic aberration primarily driven by economic and security interests, this study focuses on the considerable influence of exceptionalist ideologies and cultural factors and suggests that expansionism signifies continuity rather than discontinuity. The expansionist policies of late 19th-century U.S., demonstrated through the control of Cuba and colonization of the Philippines, were an extension of the Manifest Destiny ideology. While realists, along with social reformers, drove these policies, the exceptionalist belief in America's special mission to export liberal democracy played a key role. This ideology also directed the post-expansion shift towards restraint, showcasing a pattern of “intervention followed by restraint,” evident in the World Wars, the Vietnam War, and the Iraq War. An ideology-centered perspective of state diplomacy also proves valuable in comprehending U.S. foreign policy and the rivalry between the U.S. and China. The rivalry between the U.S. and China is not merely a clash of military power and economic interests, but also a clash of different myths.