Delaware, with 112,216 people, was the smallest and least consequential of the Border States, but if it combined with Maryland (687,049), the federal capital would be both cut off and in danger of being captured. Kentucky, with 1,115,684 persons, was vital to the Union cause. So long as it possessed Kentucky, the Union would be on the offense in the West; if it lost Kentucky, all sorts of terrible trouble might emerge. But as important as Kentucky was, Lincoln may have misjudged, because Missouri was even more important.

The 1,182,012 persons of Missouri represented a fascinating mixture of the North, South, and West, as well as the old and the new. Until about 1845, Missouri had been an unrepentant slave state, whose politics were guided by Virginians and North Carolinians who had emigrated west a generation earlier. But by 1861, the German and Irish immigrants of St. Louis outnumbered the “old” immigrants from the Southern states, and their sentiments were strongly for the Union and against slavery. This did not mean that Missouri was a pushover, however; it meant that the Show-Me State would remain divided throughout the war.