Adding new states to the Union became an issue for the Union because it raised questions about the balance of power between the Northern and Southern regions of the country. The Northern states, which were more industrialized and had a larger population, generally favored the admission of new states that would be likely to support their interests and strengthen their political power. In contrast, the Southern states, which were heavily dependent on agriculture and had a smaller population, generally opposed the admission of new states that would shift the balance of power away from them. This tension between the North and South was one of the factors that led to the American Civil War.