Explanation: One of the arguments during the 1860 presidential elections was over whether US territories could choose to be free or slave territories. “Popular sovereignty” was the rallying cry of many pro-slavery advocates - but which relied on the presumption that the people of a US territory could not, lawfully, prevent slavery from taking root in their territory. Thus making it more a presumption that slavery was part of every US territory, rather than actually ‘leaving it up to the people’.