The capture of the following railroad center prepared the north to divide the south in half:
vicksburg
new orleans
richmond
chattanooga

Vicksburg

Explanation:

The capture of Vicksburg gave the Union major advantage, with that they got complete control of the Mississipi river and were able to divide the Confederacy into two parts. It was so important that even President Lincoln had mentioned the importance of the city: "Vicksburg is the key, the war can never be brought to a close until that key is in our pocket."

b. sec, foreign relations

i would say your answer is a)

sorry if im wrong