As slavery expanded into the newly acquired territories in the West, the North realized that the increasing number of Southern states (due to admission of new slave states) could upset the delicate balance of power in Congress and give disproportionate representation to interests that supported slavery. This power would allow the South to dominate political decisions, including trade policies, economic development, and the admission of new states, at the expense of the non-slaveholding North. To prevent this influence, some Northerners supported measures like limiting the spread of slavery to maintain their own political weight and shape national policy accordingly.