Slavery existed in every U.S. state when the Constitution went into effect in 1789. Some of the Northern states, however, soon began outlawing the practice so that by 1827 the country was divided into a South that had slavery and a North that did not.

Meanwhile, by the 1830s the country’s two political parties – the Democrats and the Whigs – had lots of office holders in both the northern and southern sections of the country.

That began to change in 1854 when the Whigs became the Republicans and embraced a concept called “free soil.” That meant that as the country moved westward, the new state...