In April 1861, shortly after the Civil War began with the bombardment of Fort Sumter by rebel forces, Walker predicted that Washington, D.C. and Boston would fall to the Confederacy before May 1 of that year. However, this never happened. The only time that General Robert E. Lee's army ever invaded the North was his Pennsylvania Campaign, which ended at the Battle of Gettysburg, which the Union forces won. The Confederacy would never again attempt to invade the Union after that.