What Union victory in July 1863 split the Confederacy along the Mississippi River?

The Union victory in July 1863 that split the Confederacy along the Mississippi River was the Siege of Vicksburg.

Union Major General Ulysses S. Grant’s Army of the Tennessee captured Vicksburg, Mississippi, after a campaign of maneuvering and a 46-day siege. Confederate Lieutenant General John C. Pemberton surrendered the city and its garrison on July 4, 1863, giving the Union control of the last major Confederate stronghold on the Mississippi River.

Vicksburg’s fall cut the Confederacy’s Trans-Mississippi Department—including Arkansas, Louisiana west of the river, and Texas—from the rest of the Confederate states. The nearby surrender of Port Hudson, Louisiana, on July 9 completed Union control of the river. Together, these events fulfilled a central objective of the Union’s Anaconda Plan.

A common mix-up is the Battle of Gettysburg, fought at nearly the same time and often paired with Vicksburg as a turning point. Gettysburg stopped Robert E. Lee’s invasion of the North; Vicksburg severed the Confederacy’s internal communications and divided its territory.