The country now known and constituted as the United States began life as a series of transplanted colonies of Europeans. They forged new societies along the Atlantic coastline of North America, and they maintained constant contact with their home countries across the ocean. Thus it is little surprise that, for several centuries, the American worldview held Europe as its main ideological and cultural reference point. This Eurocentric perspective has been reflected in the historiography, most recently in the influential Atlantic World school of early modern history which sees the Atlantic coastlands of the Americas, Europe and Africa as an integrated, systemic whole.

Yet the continental United States borders another ocean, the Pacific, that has played an equally important role in the nation's political and economic development. The Atlantic World may have been important, but so too were what Matt K. Matsuda has called the “Pacific worlds”. From the earliest days of the republic, statesmen like John Quincy Adams believed that the United States must expand westward or perish. If the Atlantic marked the natural beginnings of the nation, the Pacific coast was its logical, indeed necessary, conclusion. So important was the Pacific terminus that Adams pursued westward expansion even though it exacerbated sectional tensions over slavery between the North and the South.