Why didn't the Confederacy want African Americans in their army?

They thought if they gave slaves weapons they would rebel.

Actually, near the end of the Civil War, almost a century later,

plantation owners decided they might have to fill in the ranks in

the Confederate Army with slaves because they ran out of white men

to fill in the ranks.

until the last weeks of the war, the Confederate Congress expressly forbade arming enslaved African Americans, who made up the vast majority of the black population in the South. Given white southerners' longstanding fears of a slave uprising

Explanation:

so basically, they were scared of them rebelling