The union’s manpower advantage over the confederacy: a. proved essential for the success of grant’s attrition strategy. b. was rather slight. c. existed only because the union had lower draft requirements than the confederacy. d. although substantial, did not matter in determining the war’s outcome. e. was short-lived once the confederacy began using slaves as soldiers.

a. proved essential for the success of Grant’s attrition strategy.

Explanation:

               The Union is known as the "North" and the Confederacy is known as the "South".

              At the event of the American Civil War, the Union also know as the "United States of America" under the presidentship of Abraham Lincoln was opposed by 11 southern states known as the "Confederate States of America" under the presidentship of Jefferson Davis.

               Abraham Lincoln believed that he could win over the Confederacy states until and unless he have control over the border states, mainly Maryland.

                Union's man power was more as they had nearly 20 states associated with them.

               The Union in order  to win over the Confederacy States made strategies to gradually reduced the power of the Confederacy States.

               Thus the advantage that the Union's soldier or manpower have over the Confederacy has proved to be essential for the success of Grant’s attrition strategy.

Hence the answer is

a. proved essential for the success of Grant’s attrition strategy.

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