What was the cause of the disagreement over new states being free states or slave states?

The disagreement over whether new states should be free or slave states stemmed from the broader conflict between Northern and Southern states over the institution of slavery. The Missouri Compromise of 1820 exemplified this tension, as it attempted to maintain a balance between free and slave states in Congress. Southern states wanted to expand slavery into new territories to preserve their economic interests, while Northern states aimed to limit its spread, leading to fierce political and social divisions. This conflict ultimately contributed to the tensions that fueled the Civil War.