The Siege of Vicksburg was a pivotal military campaign during the American Civil War that took place from May 18 to July 4, 1863, where Union forces led by General Ulysses S. Grant besieged the Confederate-held city of Vicksburg, Mississippi. This siege was critical as it effectively split the Confederacy in two and gave the Union control over the Mississippi River, significantly impacting supply lines and troop movements for both sides.