The Kansas-Nebraska Act eliminated the Missouri Compromise line of 1820, which the Compromise of 1850 had maintained. Settlers could now vote whether they wanted their state to be slave-free. The primary result was that thousands of zealous pro-slavery and anti-slavery advocates moved to Kansas to influence the vote, creating a dangerous and ultimately deadly mix. The most famous and infamous of them all was John Brown, one of the most controversial men in American history.
As Union commander George McClellan moved the Army of the Potomac up the Peninsula in early 1862, the Union army still had a nearly 2-1 advantage in manpower, so Army of Northern Virginia commander Joseph E. Johnston continued to gradually pull his troops back to a line of defense near Richmond as McClellan advanced. In conjunction, the Union Navy began moving its operations further up the James River, until it could get within seven miles of the Confederate capital before being opposed by a Southern fort.