Trench warfare
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
Robert E. Lee
Grant eventually was able to stealthily move his army across the James River. After stopping a Union attempt to capture Petersburg, Virginia, a vital railroad link supplying Richmond, Lee's men built elaborate trenches and were besieged in Petersburg, a development which presaged the trench warfare of World War I. Lee attempted to break the stalemate by sending Jubal A. Early on a raid through the Shenandoah Valley to Washington, D.C., but Early was defeated early on by the superior forces of Philip Sheridan. The Siege of Petersburg lasted from June 1864 until March 1865, with Lee's outnumbered and poorly supplied army shrinking daily because of desertions by disheartened Confederates.