Given its importance, it's somewhat surprising in retrospect that the Union managed to capture New Orleans in an easier manner than places like Vicksburg and Atlanta. Admiral David Farragut's naval forces battered their shaky Confederate counterparts and were able to get over a dozen ships upriver past a couple of crucial Confederate forts along the Mississippi. By May 1862, Union forces occupied the city and General Benjamin Butler became its military governor, leaving the last true bastion of Confederate defenses on the Mississippi at Vicksburg. When Grant captured that in July 1863, the Union controlled the entire river and essentially cut the Confederacy in two.
In many ways, the occupation of New Orleans for the rest of the war is as intriguing a story as the campaign to capture it. Butler was a political general, and while he would go on to be a politician in the North after the war, he became the most reviled man in the South as a result of his reign in New Orleans. During a governorship that helped earn him the moniker "Beast," Butler became notorious for several acts, including seizing a massive amount of money that had been deposited in the Dutch consul's office. But it was General Order No. 28, which said any woman in town who insulted a member of the Army would be treated like "a "woman of the town plying her avocation" (in other words, she'd be treated as a prostitute) that earned widespread condemnation across the nation, and even abroad in England. Butler was considered so brutal in the South that Confederate president Jefferson Davis personally ordered that he should be executed if he was captured. As it turned out, he never was, and when he was recalled east, he served in commands for the duration of the war before going on to a distinguished political career.
The only domino left to fall was the stronghold of Vicksburg, and both sides knew it. The Union Army of the Tennessee, led by Ulysses S. Grant, would spend months trying to encircle the city and eventually force John Pemberton's Confederate army to surrender. Grant eventually succeeded on July 4, 1863, but since it came a day after the climactic finish of the Battle of Gettysburg, Vicksburg was (and still is) frequently overlooked as one of the turning points of the Civil War. In fact, had the Confederate's military leadership listened to Longstreet, who advocated detaching soldiers from Lee's army to head west and help the Confederates deal with Grant or Rosecrans in that theater, the Battle of Gettysburg might never have happened.
While many read about the siege of Vicksburg in the summer of 1863, as well as the desperate straits the Confederate soldiers and Vicksburg residents found themselves in, Grant's initial attempts to advance towards Vicksburg met with several miserable failures, and it took several months just to get to the point where the Union forces could start a siege. First, Grant's supply base at Holly Springs was captured, and then an assault launched by Union General Sherman at Chickasaw Bayou was easily repulsed by Confederate forces, with serious Union casualties resulting. Grant then attempted to have his men build canals north and west of the city to facilitate transportation, which included grueling work and disease in the bayous.
On April 30, 1863, Grant finally launched the successful campaign against Vicksburg, marching down the western side of the Mississippi River while the navy covered his movements. He then crossed the river south of Vicksburg and quickly took Port Gibson on May 1, Grand Gulf on May 3, and Raymond on May 12. Realizing Vicksburg was the objective, the Confederate forces under the command of Pemberton gathered in that vicinity, but instead of going directly for Vicksburg, Grant took the state capital of Jackson instead, effectively isolating Vicksburg. Pemberton's garrison now had broken communication and supply lines.
