Question

Why was there such a large debate in Congress every time a U.S. territory was ready to become a state?

Answer 1

Answer: When the United States was still gaining more states, congress had a debate if the state should be a slave state or a free state. In slave states, slavery was legal while in free states slavery was illegal. Obviously, the slave states were also conservative while the free states were more liberal, so there was a debate of that too, but the bigger debate was over slavery and its legality. Assigning states to be slave or free was just a bandaid on a gunshot wound as the U.S congress hadn't made the choice of wether slavery would be illegal or not in the whole continental United States.