Why great powers expand in their own neighborhood: Explaining the territorial expansion of the United States 1819-1848

This article attempts to identify the causes of intraregional great power expansion. Using the state-to-nation balance theory we argue that, in many cases, such great power expansion can be explained as being the result of the incongruence within a given region between the nationalist aspirations and identities of the various peoples inhabiting it and the region's division into territorial states. The existence of the external type of such incongruence within a great power (that is, a pan-nationalist ideology) turns it into a revisionist state eager to expand, using all means available, in order to "resolve" this incongruence. In addition, this incongruence also creates various nationalistic trans-border groups (like terrorists, private military expeditions/filibusters, settlers, etc.). Often these groups try, through various independent efforts (usually in nearby weak states), to achieve these revisionist goals as well, thus complementing and aiding the revisionist great power's own efforts. After demonstrating the weaknesses in other existing explanations, this argument is illustrated in the case of the territorial expansion by the United States in the Southwest at the expense of Mexico in the second quarter of the nineteenth century.