Because of the mistakes committed by Hooker. They were:
1 - He ordered to the VI and I Corps successful landed at Fredericksburg after crossing the River Rapahannock on April 29, 1862, to form a strong bridgehead limiting themselves to defend it. Therefore they remained idles on the place.
2 - In the evening of the same day he sent the whole Stonemans's Cavalry Corps, out of 1,250 men, to carry a raid behind the Confederate lines, thus depriving his army of the indispensable support of scouting and covering.
3 - After brilliantly managing to seize the pivotal position of Chancellorsville, with 54,000 men, after a while increased up to 75,000, Hooker claimed " to wait for Lee's attack to come". Instead to carry hastily on the outflanking movement towards Fredericksburg, he advanced in a very slowly and hesitant way as he were being caught by "the fog of war". Evidently the fatal effects of the absence of his cavalry began to be felt.
Lee took advantage of those mistakes and decided to split his army into two part.
He left 10,000 men at Fredericksburg to guard and keep at bay the inactive Union Corps standing there.
He sent four divisions (McLaws of I Corps, A.P. Hill, Rodes and Colton of II Corps and Stuart's Cavalry Corp., to join the division Anderson (for a total of about 52,000 men) and form a defensive line at Tabernacle's Church to face and check Hooker's 75,000.
When his divisions clashed against the Confederate entrenchments, finding a sturdy resistance, Hooker, ignoring how strong the opponent were and lest of being outflanked, ordered to withdraw back to Chancellorsville, where the army had to stand on the defensive.
At that point, Lee received intelligence from his cavalry, that informed that the extreme Union wing near Wilderness Church was based "on the nought" and therefore susceptible to be outflanked and attacked from the back.
He then decided to further split his army in front of the enemy and ordered his II Corps and Fitzhugh's cavalry division (30,000 men) under Stonewall Jackson to put in motion the relevant displacement and carry out the assault, , which was successful and turned over the battle in favor of Confederate army.
The Union won the Battle of Vicksburg, led by General Ulysses S. Grant
The South won in the battle of Chancellorsville.
Joe Hooker moved the Union Army of the Potomac to bring Lee to battle, and threaten Richmond. But Lee out foxed him, won the battle, and Hooker retreated.
At Chancellorsville the Army of Northern Virginia(Confederate) commanded by General Robert E. Lee engaged and defeated the Army of the Potomac(Union) commanded by General Joseph Hooker.
The Battle of Chancellorsville resulted in a Confederate victory, but casualties on both sides were heavy. Also, Thomas 'Stonewall' Jackson was mortally wounded in this battle.
The union won
At the battle of Chancellorsville, it was General Robert E. Lee for the Confederacy and Joseph Hooker for the Union.
8,000
About 4,500 men died for the Union side in the battle of Chancellorsville.
General Joseph Hooker (Union)
Chancellorsville
Of all arms, around 130,000.
it was a battle during the Civil war between the Union And Confederate forces. Confederates won the battle.
It was one of the attempts by the Union to capture the Confederate capital, Richmond.
Around 133,000 Union, and 61,000 Confederates.
Major General Joe "Fighting Joe" Hooker was the commander of the Federal Army of the Potomac at Chancellorsville.
Confederacy lost General Thomas (Stonewall) Jackson at the battle of Chancellorsville.