Which of the following is a reason why blacks were not allowed to serve in the
Union Army at the start of the Civil War?

Blacks tended to side with the Confederacy rather than the US

Former slaves were not willing to fight what they believed was a "white man's
war".

There was no way to recruit slaves in the South to fight

Fear that it would push border states to secede and join the Confederacy

C: Fear that it would push border states to secede and join the Confederacy.

Explanation: I took the test, also in the class slides it says: President Lincoln also realized that arming former or escaped slaves  could also push the border states into seceding and supporting the  efforts of the Confederacy.

answer: (fluidity)is the correct answer.

explanation: because of this characteristic, success on the battlefield depends in large part on the ability to adapt to proactively change events to our advantage as well as to react quickly to constantly changing conditions