Union troops, ordered by President Abraham Lincoln, began a crucial 25-mile march into Virginia with the anticipation of confronting Confederate forces at Bull Run. This movement was part of a broader strategy to establish dominance in the southern states and to quickly quell what the Union hoped would be a short rebellion. The area near Bull Run was strategically important as it held routes that could lead to the Confederate capital of Richmond. Lincoln's decision reflected a growing urgency to demonstrate military strength and resolve following a series of skirmishes and the mobilization efforts that had characterized the early months of the Civil War.

The march culminated in what would become the First Battle of Bull Run, fought less than a week later on July 21, 1861. As troops mobilized, the landscape was fraught with tension as both sides prepared. Nervous recruits and seasoned soldiers alike were drawn into the conflict, and the ensuing battle would reveal the realities of war far beyond the expectations of quick victories.

Furthermore, the initial clash marked a pivotal point in the Civil War, exposing the challenges of early military strategies and the necessity of better training and organization for Union forces. The march highlighted the rapid progression towards full-scale warfare as volunteers flooded into regiments, and the dreams of a short conflict began to fade. The First Battle of Bull Run would also foreshadow the prolonged nature of the Civil War; the implications of the Union march were felt not only in military terms but also in shaping public perception of the war's projected length and violence.