Final answer:
The rise of the Republican Party was due to opposition to the spread of slavery. The party defined its position by advocating for the limitation of slavery to where it already existed and opposing its expansion into new territories.
Step-by-step explanation:
The rise of the Republican Party can be attributed to the growing opposition to the spread of slavery in the United States, particularly in the Western territories. The formation of the Liberty Party, Free-Soil Party, and finally, the Republican Party, all reflected the increasing concern over the expansion of slavery. The Republican Party defined its position on the slavery question by advocating for the limitation of slavery to where it already existed, and opposing its expansion into new territories.