Answer: They were opposed to it.
Step-by-step explanation:
The Republican party was formed by people opposed to slavery in the United States. Seeing however, that they could not abolish it in the U.S. due to the power of the Southern States in Congress, they opted instead to limit its spread into the U.S. territories that were yet to be states.
This excerpt shows them explaining why it was necessary that they limit slavery in the territories. The Republican party became increasingly powerful and this worried the Southern States so much so that when Republican Abraham Lincoln became President, they seceded because they thought he would move to abolish slavery in all of the U.S.