International migration affected regional relationships in the pre-civil war period as most new arrivals were settling in the northeast or old northwest, tying those regions socially and economically.
On the other hand, the south remained anchored in an economic system that was unfavorable to capitalist development (mechanization and hiring of workers was cheaper than the maintenance of slaves). The Democratic Party would be the defender of slavery. This party had led the great expansion of the country to the south (activism in favor of the annexation of Mexican territory) and now stood as representative of the southern elites, which sought fundamentally the extension of the slave system and free trade for the export of raw materials and the importation of manufactured goods without barriers.
With the expansion to the West, the tension between the two economies only increased, since both systems needed such expansion in the face of the international bullish situation. The fact that seven immigrants out of eight settled in the North, added to the fact that there were twice as many whites moving from the South to the North than those who made the opposite way, contributed to the aggressive defensive policy of the South.
