the first battle of winchester was fought on may 25, 1862, in and around frederick county and winchester, virginia during the american civil war. the battle was a victory in confederate army major general thomas j. "stonewall" jackson's campaign through the shenandoah valley. jackson enveloped the right flank of the union army under major general nathaniel p. banks. the union forces retreated across the potomac river into maryland. due to confusion among confederate commanders, jackson was unable to pursue banks into maryland.