Why did Grant decide to attack Jackson before attacking Vicksburg?
General Pemberton had his army defending Vicksbug. General
Johnston had more troops oustide of Vicksburg and these threatened
the Union with attack from the rear. Gen Grant may have thought he
could take Vicksburg defenses by attacking from the river or from
Port Hudson side. But he realized he had to lay a siege against
Vicksburg. To do this, he had to defeat the forces that were
outside of the city and surround the city. The Battle of
Jackson(May 14) was fought to cut off re-inforcements from giving
aid to the Confederates at Vicksburg. Then final battle occurred at
Battle of Champion's Hill(May 16). This forced the Confederates
back into the Vicksburg defenses. Link to a Map of Union advance:
http://en.wikipedia.org/wiki/File:VicksburgCampaignAprilJuly63.png