On April 14, 1861, following the surrender of Fort Sumter, Washington was "put into the condition of a siege," declared Abraham Lincoln. Located sixty miles south of the Mason-Dixon Line, the nation's capital was surrounded by the slave states of Maryland and Virginia. With no fortifications and only a handful of trained soldiers, Washington was an ideal target for the Confederacy. The South echoed with cries of "On to Washington!" and Jefferson Davis's...