The Confederates wanted to hold on to what they had in the East; the Union wanted to press its advantage. In the second week of July 1861, General Irvin McDowell (1818–1885) prodded his men across the Potomac and into northern Virginia.

The landscape was quite different from what the men knew; the social and economic differences between the North and the South became readily apparent. Instead of towns and villages, they found plantations and hamlets, with more real living space than expected, but many people living in mild poverty. Another eye-opener had to do with the federal troops themselves: they were, for the most part, in poor physical condition. Americans of 1861 worked harder and longer than their descendants today, but even farm boys were not accustomed to long walks: they rode hay wagons whenever possible. Therefore, as the federal troops moved into the Virginia countryside, they experienced exhaustion and the occasional case of heat stroke.