The First Battle of Bull Run
Pre-Civil War America had seen little real military action and knew nothing of war beyond fantastic
portrayals in books—the First Battle of Bull Run (known as Manassas by the Confederates) of July 21,
1861, represented a grim beginning to the Civil War and a portent of things to come.
BEFORE
First Bull Run dwarfed any other clashes
that the U.S. Army had hitherto fought.
Its use of new technology helped the
Confederacy gain advantage.
SMALL ARMIES
Washington had fewer than 17,000 men at
Yorktown, the decisive battle of the American
Revolution, and General Winfield Scott had taken
Mexico City in 1847 with an army of only about
11,000 men. At First Bull Run, Union general
McDowell led 35,000 to his opponents’ 30,000.
DEVELOPMENT OF RAILROADS
When the British invaded the American colonies,
they could not benefit from industrialized forms
of transportation, such as the railroad. This
new form of technology could be used for
defensive purposes by both sides in the Civil War.
GEORGE B. MCCLELLAN
Shortly before First Bull Run, Union commander
George B. McClellan won a few skirmishes in
western Virginia, which helped secure the
important Baltimore and Ohio Railroad, laying
the groundwork for the formation of West
Virginia. McClellan’s success before the disaster
of First Bull Run made him the natural
replacement for McDowell.
P. G. T. Beauregard at Manassas.
The Confederate leaders hoped that
the railroad in between the two
armies would allow them to move
reinforcements between both positions
more swiftly than the Union army,
which did not have access to a direct
rail connection.Line advantage
Military thinkers from the Civil War
era and modern historians call this
Confederate geographic advantage
“interior lines.” For example, if a
straight line is drawn, connecting two
points on an arc, the line is much
shorter than the arc. The Confederacy,
as the country defending the arc, had
the advantage of “interior lines” across
its territory, while the Union had to
operate on “exterior lines” outside of it.
First Bull Run was the first example of
a larger Confederate advantage in terms
of defensive positioning.T
he First Battle of Bull Run took
place at the important railroad
intersection of Manassas Junction,
Virginia. In the wide expanses of the
Confederacy, where the primitive road
network and the highly dispersed
population made it difficult for an
army to live off the countryside,
railroads were indispensable. They
carried much-needed supplies and
became strategic assets. The crossing
at Manassas Junction, where the
Orange and Alexandria Railroad met
the Manassas Gap Railroad, was a
vital line of communication—leading
south into the heart of Virginia,
and west to the agriculturally fertile
Shenandoah Valley.
The Confederacy posted two field
armies to cover these possible lines of
advance—General Joseph E. Johnston’s
force in the northern Shenandoah
Valley, numbering a little less than
10,000, and 18,000 men under GeneralEventually, the Union would find
that the best way to overcome the
Confederate advantage of interior
lines was to use its superior resources
to coordinate multiple and
simultaneous attacks along the entire
“arc” of the Confederacy’s defensive
perimeter. This goal would be
achieved to some extent by the Union
offensives of 1864, which eventually
brought the war to an end. However,
as early as First Bull Run, General
Winfield Scott attempted such a
coordinated strategy on exterior lines
when he ordered Major General
Robert Patterson in the Shenandoah
Valley to advance and try to prevent
Johnston from moving his troops
eastward from the valley to reinforceApproximate number of
Confederate casualties.Approximate number of
Union casualties.2,000
3,000
Retreat at Bull Run
After the battle, the Union Army retreated in total
confusion to the fortifications around Washington.
Military wagons and the carriages of fleeing spectators
blocked their route, and many men were captured.