Trench warfare
Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition. Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side that was able to commit the last reserves to the Western Front.
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.