What does x-ing the potomac mean?

"Crossing the Potomac" is a reference to the Union Army's invasion of Virginia during the American Civil War.

In July 1861, Union General Irvin McDowell led an army of approximately 35,000 soldiers across the Potomac River from Maryland into Virginia. This was the first major offensive of the war, and it was seen as a crucial test of strength between the Union and the Confederacy.

The Confederate army, led by General P.G.T. Beauregard, met the Union forces at the Battle of Bull Run (also known as the First Battle of Manassas). The Confederate army won a decisive victory, forcing the Union troops to retreat back across the Potomac.

The Confederate victory at Bull Run had a significant impact on the course of the war. It boosted the morale of the Confederate army and gave them confidence that they could defeat the Union. It also led to calls for more troops and resources from both sides, escalating the conflict and setting the stage for the long and bloody years of the Civil War that followed.