Which statement best explains why slavery became a major national political issue as the U.S. expanded...

Which statement best explains why slavery became a major national political issue as the U.S. expanded westward?
- Western territories refused to follow federal laws about labor.
- New territories raised questions about whether slavery would expand and shift political power.
- Most Northern states wanted to replace slavery with indentured servitude.
- The Supreme Court banned slavery in all territories.
How did slave rebellions most directly affect political debates about slavery?
- They convinced most Southern leaders to support gradual emancipation.
- They led to fewer restrictions on enslaved people to reduce tensions.
- They increased Southern demands for stronger protections of slavery and harsher controls.
- They caused Congress to stop discussing slavery in public sessions.