Union soldiers expected a show of force to break resistance because they believed secession lacked broad support. Confederate states, by contrast, could draw on militia organizations maintained partly against feared slave rebellions. Those troops were not highly trained, but their units had spent longer together and knew their officers. They also received Union attacks from defensive positions while McDowell's forces arrived piecemeal, so cohesion and posture outweighed the Union's greater total manpower.
Notable Point · 7:51-10:17
Militia cohesion and defensive advantage
Union expectations of an easy march collide with Confederate militia cohesion, familiar command relationships, and the advantage of receiving piecemeal attacks on the defensive.