Final answer:
Northerners were concerned that adding more states would shift the balance of power in Congress.
Step-by-step explanation:
Northerners were concerned that adding more states would shift the balance of power in Congress. They were worried that the addition of new states would dilute the influence of the northern states and give more power to the southern states. This concern was related to the issue of slavery and the fear that new states would be admitted as slave states, further strengthening the southern states' control over the federal government.
Learn more about northerners' concerns about expanding the number of states in the United States