Why did the union struggle to take vicksburg from the confederacy

The fort was located on top of a hill and surrounded by swamps.*
The fort was far from water, which made it difficult to reach.
The fort was only approachable from one direction by land.
The fort could only be attacked from the Mississippi River.

C, because he has a direct link and profit from the trade. the fastest way by boat to transport those goods is via the panama canal.