Vicksburg was nicknamed "The Gibraltar of the Confederacy." No large Union boats could sail the Mississippi past it without drawing cannon fire and likely being sunk -- the Union had dug a canal to avoid Vicksburg but it was too shallow for big boats. Union forces under General Grant, whose star had been steadily riding since the fall of Fort Donelson had been trying for a long time to get at Vicksburg -- there had been seven failures trying to get Union forces to where they could assault Vicksburg, and all the Union did was create a growing casualty list, and public opinion that General Grant was a fool, a drunkard, or worse.
"All Grant's schemes have failed," observed Elihu Washburn, long Grant's congressional benefactor who elevated the  West Pointer to brigadier general early in the war. One newspaper editor colorfully put it (quoted in Shelby Foote, Fredericksburg to Meridian pg. 217), "Well, now, for God's sake say that Genl Grant, entrusted with our greatest army, is a jackass in the original package. He is a poor drunken imbecile. He is a poor stick sober, and he is most of the time more than half drunk, and much of the time idiotically drunk."

In answer to his critics, in his memoirs Personal Memoirs of U.S. Grant, Grant had to say (ch. 32),

I took no steps to answer these complaints, but continued to do my duty, as I understand it, to the best of my ability.

Aware of Grant's victories on the battlefield, Lincoln deftly parried rumors of Grant's drunkenness by saying, "If I knew what brand of whiskey he drinks I would send a barrel or so to some other generals." Despite the appalling casualities at Shiloh, and (false; see below) rumors of Grant's drunkenness on the battlefield, Lincoln had also said of Grant "I can't spare this man, he fights." But of the seven failures that got the Union no closer to Vicksburg, in Battle Cry of Freedom, pg. 588, historian James B. McPherson observed,

For two months Grant's army had been floundering in the mud. Many of them rested permanently below the mud, victims of pneumonia or dysentery or any of a dozen other maladies. Vicksburg stood as defiant as ever.

Union mood in early 1863 was depressed. Defending Vicksburg was John C. Pemberton, a Pennsylvania Yankee who married South and sided with the Confederacy. He was not as sanguine about the Confederacy's hopes of keeping Vicksburg as some on the Union side, certain that the Grant's thrashing about would eventually hit a soft spot. Confederate General Joseph E. Johnston was afraid of the Federals in the West; as Bruce Catton observed (ch. 2, part 2),

... General Johnston suspected that the Federals in the Mississippi Valley held a winning hand if they played it right.

He was later shown to be right, after the shedding of much blood in a high-stakes poker game between U.S. Grant and the Confederates. The Union had three options to reduce Vicksburg, where they were fighting against Confederate-favoring geography as much as gun-toting Confederates:

  1. A direct attack from the Mississippi,
  2. Pull back on Memphis, going overland, or
  3. March the army down the west side of the Mississippi, cross the river south of Vicksburg, and attack from the south and the east.

North and east of Vicksburg was the Yazoo Delta, 200 miles high and as far as fifty wide, a practically impenetrable swamp. General Sherman had tried to go this way, blundering hopelessly. About 12 miles up the Yazoo were powerful Confederate batteries at Haines Bluff.

The Louisiana shore west of Vicksburg was not much more forgiving, riven with streams and poor country roads, and on the wrong side of the river. Retreating to Memphis, Tennessee and taking the railroad down, east of the primeval Yazoo Delta made sense, but that would be an admission of defeat, and Northern public opinion would condemn the already-shaky Grant. He chose the third plan.

Grant had political considerations with which to deal as well. Henry Halleck ("Old Brains," above him in Washington) was of a cautious bent, and Grant knew he might oppose the dangerous naval expedition. The Union fleet could be lost or crippled; Grant was to place his troops where a Confederate force of unknown size might destroy them; and the Union supply line down the Mississippi was in grave danger of being snapped, leaving an entire Union army cut off.

Some on Grant's staff and other Union generals such as Sherman and General James B. McPherson opposed the dangerous plan. Sherman recommended falling back to Memphis and going down from there.

Grant's plan was thus far more dangerous than one gets from one-paragraph summaries in American history texts.